IL225937A - Thermal fiber drawing (tfd) with added core break-up process and particles therefrom - Google Patents

Abstract

A thermal fiber drawing (TFD)-based method for forming particles includes providing a multi-material fiber having at least one core including a first material and an outer first cladding layer including a second material different from the first material outside the core. TFD is used to increase a length of the multi-material fiber to form an extended multi-material fiber having an extended core such that the core diameter or other core cross sectional dimension approaches the desired particle size after subsequent break-up. The extended multi-material fiber is thermally treated under conditions that cause a breaking up of the extended core to form a plurality of core particles embedded in the cladding layer. The core particles can optionally be removed from the cladding layer. [WO2012058314A2]

Description

THERMAL FIBER DRAWING (TFD) WITH ADDED CORE BREAK-UP PROCESS AND PARTICLES THEREFROM FIELD

[0001] Disclosed embodiments relate to thermal fiber drawing (TFD)-related processing and particles therefrom.

BACKGROUND

[0002] Known approaches forming microparticles and nanopar licles generally rely on nucleation, chemical reactions, or self-assembly. The particles produced using such approaches are typically characterized by a large dispersion in the si ze and shape distribution, and are generally hampered by coalescence and agglomeration during particle growth.

SUMMARY

[0003] Disclosed embodiments include thermal fiber drawing (TFD)-based methods for the efficient and scalable fabrication of microparticles or nanoparticles. TFD is a process in which a macrostructured preform comprising a multi-material liber (outer cladding and at least one inner core) is heated and drawn into an extended length to form an extended multi material fiber. TFD has been demonstrated to be capable of producing extremely long lengths (e.g., hundreds of meters) of uniform and ordered nano-filaments, generally from glassy insulating (dielectric) materials.

[0004] Disclosed TFD-based methods processes may be contrasted from known TFD methods. In order to ensure the integrity of the core(s), in known TFD methods the preform is thermally drawn in a high- viscosity regime (> 106 Pas) and the extended multi-material fiber emerging from the heating zone is cooled quickly to arrest the development of any axial instability. In contrast, disclosed methods instead promote axial instability by maintaining the extended fiber at an elevated temperature for an extende period of time, allowing the l core(s) to break up into uniformly sized droplets which are "frozen" in situ upon cooling to form a plurality of microparticles or nanoparticles embedded in tire outer cladding. The fiber core(s) and cladding correspond to the dispersed and continuous phases, respectively. The core particles may be then released if desired by removing the cladding, such as by solvent removal.

[0005] Disclosed methods allow for the fabrication of embedded particle arrangements comprising monodisperse parLicles over a wide and selectable range of sizes, extending from about 5 nm to about 1 m, and from a variety of materials, including, but not limited to glasses, polymers, liquids, and metals. In most embodiments the particles are spherical in shape, and are molecularly smooth providing a root mean square (rms) roughness < 1 nm.

[0006] In one embodiment the core comprises a plurality of cores, and after disclosed thermally treating provides a three dimensional distribution of core particles embedded in the cladding layer. The three dimensional distribution of core particles can include includes periodicity providing a standard deviation of center-to-center particle spacing <5% of the average center to center particle spacing in at least a first and a second dimension transverse to the length direction of the extended multi-material fiber. Disclosed embodiments are topdown non-litbographic approaches which may be contrasted with conventional techniques for forming such particles that are bottom -up and rely on nucleation, chemical reactions, or selfassembly of the particles. 225937/2 BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a flow chart that shows steps in an example TFD-based method for the efficient and scalable fabrication of microparticles or nanoparticles, according to an example embodiment.

[0008] FIG. 2A shows an example fiber tapering setup, FIG. 2Ba scanned optical micrograph of a fiber cross section with a 20-pm core diameter, FIG. 2Ca scanned image of a typical fiber taper, while FIG. 2D shows a magnified scanned image of the taper center (corresponding to the dotted box in FIG. 2C) showing the core broken into a periodic string of core droplets oriented along the axial (drawing) direction, according to example embodiments.

[0009] FIGs. 3A-E are scanned optical micrographs of the side view of fiber tapers produced at different temperatures, but with the same tapering speed (2 mm/s) and tapering distance (15 mm) showing different stages of the core breakup process, according to example embodiments.

[0010] FIGs. 4A and 4B are scanned SEM micrographs of twelve 20 micron-diameter intact glass cores exposed from a 1-mm-outer-diameter fiber cross section, according to example embodiments. .

[0011] FIG. 5 is a scanned high-magnification SEM micrograph of a fiber including 27,000 cores each of 200 nm in diameter, with stacked fibers in the preform producing a hexagonal lattice (see dashed lines). At each lattice site 80 200-nm glass cores are located as shown in the inset.

[0012] FIG. 6A is a scanned SEM micrograph of a 1-mm-diameter fiber cross section containing 80 7pm diameter cores, FIG. 6B is a higher-magnification scanned SEM micrograph of the 80 cores, G=As2Se3 and P= polyethersulfone (PBS). FIGs. 6C and 6D are scanned transmission optical micrographs of the fiber side view before and after breakup (via global heating), respectively, showing the resulting spatial distribution of particles immobilized in the cladding (scaffold) is well-ordered in all 3 dimensions.

DETAILED DESCRIPTION

[0013] Disclosed embodiments in this Disclosure are described with reference to the attached figures, wherein like reference numerals are used throughout the figures to designate similar or equivalent elements. The figures are not drawn to scale and they are provided merely to illustrate the disclosed embodiments. Several aspects are described below with reference to example applications for illustration. It should be understood that numerous specific details, relationships, and methods are set forth to provide a full understanding of the disclosed embodiments. One having ordinary skill in the relevant art, however, will readily recognize that the subject matter disclosed herein can be practiced without one or more of the specific details or with other methods. In other instances, well-known structures or operations are not shown in detail to avoid obscuring structures or operations that are not well-known. This Disclosure is not limited by the illustrated ordering of acts or events, as some acts may occur in different orders and/or concurrently with other acts or events. Furthermore, not all illustrated acts or events are required to implement a methodology in accordance with this Disclosure.

[0014] Notwithstanding that the numerical ranges and parameters setting forth the broad scope of this Disclosure are approximations, the numerical values set forth in tire specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements. Moreover, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein. For example, a range of "less than 10" can include any and all sub-ranges between (and including) the minimum value of zero and the maximum value of 10, that is, any and all sub-ranges having a minimum value of equal to or greater than zero and a maximum value of equal to or less than 10, e.g., 1 to 5,

[0015] Disclosed embodiments include TFD-based methods applied to multi-material fibers for the efficient and scalable fabrication of microparticles or nanoparticles. Disclosed methods include an added thermally-based process applied to the extended multi-material fiber having an extended core generated by TFD, that results in the extended core breaking up into a plurality of microparticles or nanoparticles that are embedded in the cladding layer. Disclosed processes may be contrasted with known TFD processes by the addition of a thermally-based process after tire TFD of the multi-material fiber that has been found to result in the extended core of the drawn multi-material fiber breaking up into a plurality of particles.

[0016] FIG. 1 is a flow chart that shows steps in an example TFD-based method 100 for the eficient and scalable fabrication of microparticles or nanoparticles, according to an example embodiment. Step 101 comprises providing a multi-material fiber having at least one core comprising a first material and an outer first cladding layer comprising a second material different from the first material outside the core. The first and second material generally have similar softening temperatures that allows for the first and second materials to be consolidated together and then co-drawn from the same fiber preform, such as a softening temperature within 50 °C of one another. Step 101 can comprise preparing a multi-material macroscopic preform with a core assembled from the intended particle constituent materials encased in a scaffold material that provides a cladding layer.

[0017] Step 102 comprises TFD the multi-material fiber to increase a length of the multi-material fiber to form an extended multi-material fiber having an extended core such S that the core diameter (or other cross section dimension) in the extended core is reduced to approach that of die desired particle size. The temperature selected is high enough to allow for the preform to be drawn continuously into a fiber. The fiber can be rapidly cooled (e.g. with active cooling) after TFD to arrest the development of axial instability. The TFD can optionally include two or more TFD steps.

[0018] Step 103 comprises thermally treating the extended multi-material fiber under conditions (e.g., temperature, time, and tapering speed) that cause an axial breaking up of the extended core to form a plurality of core particles embedded in the cladding. The maximum temperature utilized in step 103 is generally higher than the maximum temperature used in step 102, such as by a temperature higher by at least 10 °C. In this step die thermal treatment of the drawn fiber controllably induces the break-up of the extended core(s). In a typical embodiment the extended core breaks-up into an orderly (periodic) sequence of oriented, smooth- surfaced structured spherical particles held immobile in the cladding. The thermally treating can comprise holding a temperature fixed along a fiber axis of the multi-material fiber, and using a sufficient heating time to form the plurality of core particles. In another embodiment the thermally treating can comprise applying a temperature gradient along a fiber axis of the multi-material fiber.

[0019] In optional step 104, the core particles may be released from the cladding. For example, the core particles embedded in the cladding may be released by dissolving the cladding material in a suitable solvent that does not affect the core particles.

[0020] Although not necessary to practice disclosed embodiments, the breaking up of the extended core(s) of the drawn multi- aterial fiber into a plurality of particles is believed to be based on Plateau-Rayleigh (PR) capi llary instability during the TFD-based tapering of a multi-material fiber. In one particular embodiment the fiber core can comprise a glass and the cladding comprises an amorphous thermoplastic polymer. PR instability is believed to be manifested in the breakup of the core into a periodic string of size-tunable micro-scale droplets embedded along the fiber axis. As disclosed above, size tuning can be provided by TFD processing such that the extended core(s) has a cross sectional dimension (e.g., a diameter) that approaches the desired particle size.

[0021] Fiber tapering is a process that allows for obtaining a wider range of parameters as compared to fiber drawing. Referring to FIG. 2A, steps in an example fiber tapering apparatus 100 are shown. In fiber tapering a fiber 110 is inserted in a movable heating zone 115 for a fixed (predetermined) time before both ends of the fiber are pulled symmetrically in opposite directions by the motor 130 together with rollers 132, cabling 133 and end holders 134 as shown in FIG. 2A.

[0022] There are generally at least three controllable fiber tapering parameters that may be used for process control of TFD. A first parameter is the temperature T, which determines the viscosity of the respective fiber materials. The second parameter is the tapering distance L which is defined as the length by which the fiber is elongated after softening, that determines the final diameter (or other cross sectional area) of the fiber taper. A thir parameter is the tapering speed v, which determines the dwelling time in the heating zone II 5. Once the tapering ends, the heating zone is removed and the extended fiber can be cooled, such as in air. Alternatively, active cooling may be used.

[0023] There are generally at least two parameters other than time that may be used for process control of thermally treating of the extended multi-material fiber to cause a breaking up of the extended core to fonn a plurality of core particles. A first parameter is the temperature T, which as with TFD determines the viscosity of the respective fiber materials. A second optional parameter is the tapering speed v.

[0024] An example fiber used in experiments performed comprised a glassy chalcogenide semiconductor (AszSe- ) core having a diameter in the range 5 pm - 20 pm with a thermoplastic polymer cladding comprising PES having an outer diameter of 1 mm as depicted in FIG. 2B. An example of a typical taper is shown in FIG. 2C, with the central tapered section 230 observed so that the continuous and uniform extended glass core shown evolved after post tapering thermally processing into a periodic string of core droplet particles 237 as depicted in FIG. 2D. It is noted that the apparent size of the core in FIG. 2C and the droplets in FIG. 2D are larger than their actual sizes due to magnification resulting from the curvature of the fiber outer surface.

[0025] Disclosed embodiments also include compositions of matter comprising a plurality of core particles embedded in a scaffold. In one embodiment an embedded particle arrangement comprises a multi-material fiber having a length > one hundred times its cross sectional area, where the multi-material fiber includes a cladding material providing a continuous phase for said multi-material fiber, and a plurality of particles along at least a portion of tire fiber length embedded in the cladding material. The plurality of particles are separated from one another, have a median size from 5 nm to 1 mm, are spherical in shape, and are molecularly smooth providing a root mean square (rms) roughness < 1 nm.

[0026] The cladding material in one embodiment comprises a polymer, such as a thermoplastic polymer. For embodiments corresponding to use of performs including a plurality of cores, the plurality of particles are arranged in a three dimensional distribution. The three dimensional distribution of particles can include periodicity providing a standard deviation of center-to-center particle spacing <5% of the average center to center particle spacing in at least a first and a second dimension transverse to tire length dimension of the multi-material fiber. As described above, the transverse periodicity is controllable at the fabrication stage through the stack-and-draw process. A periodicity of < 15% (such as about 10%) of the average center-to-center particle spacing can also be provided in the length dimension of the multi -material fiber. The plurality of particles can be uniformly sized providing a <10% standard deviation in particle size with respect to an average (mean) size of the particles.

[0027] In one embodiment, the particles in the embedded particle arrangement include a first hemisphere comprising a first material and a second hemisphere comprising a second material different from said first material. For example, the first material can comprises a first glass and the second material comprises a second glass.

[0028] Disclosed particles can comprise spherical particles including a first hemisphere comprising a first material and a second hemisphere comprising a second material different from the first material. In this embodiment the first material can comprise a first glass and the second material a second glass different from the first glass to provide "Janus particles" that are generally defined as spherical glass particles with one of the hemispheres being one material and the other hemisphere being another material. Disclosed processing may also be extended to multiple sectors (e.g., 3, 4, 5 ...) of a cylinder to form spherical particles with more sophisticated sub-structure.

[0029] Applications for disclosed particles are numerous. Example applications include cosmetics, biomedical (e.g., drug delivery), chemical and biological catalysts, and paints ( particles are held as a colloid in a solution).

EXAMPLES

[0030] Disclosed embodiments are further illustrated by the following specific Examples, which should not be construed as limiting the scope or content of this Disclosure in any way.

[0031] Example parameters tested include an initial As2Se3 core diameter of 40 p and PES cladding tapered at a fixed speed v=2 m /s and tapering distance d 15 mm, but with varying temperature T. As2Se3 is known to has a melting point of about 360 °C and a glass transition temperature of about 180 °C. The PES used had a glass transition temperature of about 230 °C. When the fiber temperature rises sufficiently above both of the glass transition temperatures and the viscosity decreases sufficiently, PR instability is believed to be initiated through perturbations at the core/cladding interface.

[0032] Referring to FIGs. 3 A and 3B, it was found that at rel tively low temperatures, such as 261 °C and 264 °C, respectively, the viscosity of tire As2Se3 core is relatively large and the extended core remained intact during tapering, so that no core droplets were observed. However, as the temperature was increased, a gradual growth in the PR instability shown began at about 268 °C apparently resulting in the periodic string of periodic core droplets shown being formed, as shown in PIGs. 3C-E.

[0033] Static heating was also studied. Static heating as used herein refers to the only parameter being varied is tire temperature (no pulling/tapering). The Inventor measured the breakup time t over the range of temperatures for fibers with initial core diameter pm, where t was measured from the start of heating until initiation of breakup. The measurements revealed that t depends inversely on temperature.

[0034] In order to analyze these results quantitatively, the inventor adopted as a model the linear stability analysis of Tomotika [S. Tomotika, Proc. Roy. Soc. Loud, A 150, 322 (1935)], which describes a stationary viscous thread embedded in an unbound viscous fluid. According to this analysis, perturbations at the interface between the two fluids (core and cladding here) grow on a time-scale t that depends on the perturbation wavelength l, the viscosities of the two fluids (glass core hk and polymer cladding hr, tire thread diameter (core diameter D, assuming an unbound cladding for simplicity), and surface tension y. The wavelength with the largest growth rate (minimum t quickly dominates the instability and results in the core breaking up into a periodic sequence of droplets with separation l. In calculations performed by the Inventor the following values of tire parameters were used: D-IOmpi, surface tension between As¾Se and PBS g=0.1 N/m and hr=305 Pa-s for PES. While the temperature dependence of hr over the temperature range of interest was ignored, h;, for As2Se3 changes considerably over the same range and was obtained from an empirical Arrhenius formula. Using these values tire instability growth time as a function of temperature was calculated and the results compared the results to the experimental data. The predictions of the Tomotika model are in quantitative agreement with the data. The Inventor further calculated t over the same temperature range for other initial core diameters. To a reasonable degree of accuracy, it was found that x depends linearly on D at a fixed temperature.

[0035] Tire inventor also examined the effect of each fiber tapering parameter (L, T, and v) while holding the other two parameters fixed. The Inventor adopted a simple model for this system based on a quasi-static extension to the static Tomotika model. This model decouples the effect of heating on the core from the dynamics of tapering. The Inventor thus used the static results for the temperature-dependent instability time x and then added the geometric effect of size change during tapering. The inventor found that this model yields results in quantitative agreement with our observations despite its simplicity within the margin of error in the measurements performed.

[0036] The effect of tapering distance L while holding v=l m /s and T=285°C was studied. The static results indicated that breakup occurs after about 80 s at this temperature with the initial core diameter D=10 pm. As the diameter decreases during tapering, x decreases accordingly. The Inventor found that the core remains intact until L=21 mm at which point it breaks up into a series of droplets with an average separation of 7.1 pm. After breakup has occurred in the taper, further elongation was found to only increase the droplet separation.

[0037] Making use of the above-described quasi-static model, and making use of the approximately linear relation between x and diameter D, an estimate for D at the moment of breakup can be generated. Taking x-21 s, Dfinai ~ 2.6pm is estimated. This estimate depends only on the measured instability time and the assumptions of the static Tomotika' model. The Inventor also arrived at an independent estimate from a different route. Geometric considerations coupled with the simplifying but reasonable assumption that the temperature of the heating zone is uniform and the taper material exiting the heating zone cools down immediately lead to the initial and final core diameters being related by a factor of the form e where h is the length of the heating zone. Thus 2.9pm, consistent with the considerations described above. The last data point (at b=27pm) was higher than expected since the fiber undergoes rapid plastic deformation before mechanical fracture with further tapering.

[0038] The effect of T for fixed v=l mm/s and d-23 mm was next considered where the final taper diameter remains approximately constant. At low temperatures, the viscosity of the core was found to be relatively large and the core to remain intact. As the temperature increased, the PR instability grows until droplets are formed and the average period of the droplets increases with temperature. This may be understood as follows: viscosity decreases exponentially with T and the Tomotika model indicates that lower viscosity leads to linearly shorter instability time. The instability thus develops quickly at a larger diameter corresponding to a longer period. The period hence will exponentially increase with temperature. Furthermore, if the breakup occurs early on in the tapering process at higher temperature, then further tapering leads to further separation between the core droplets.

[0039] The effect of v while holding d=23 mm and T=285°C was next considered. The final diameter of the fiber taper is also approximately constant. At high speeds, the dwelling time may be less than t for the final core diameter, and the core thus remains intact. At lower speeds, the fiber dwells for a longer time in the heating zone thus having the opportunity to reach t and thus breakup. The breakup of the larger-diameter core during tapering results in longer period, and then the droplets further separate if the tapering process continues. The period was found to be inversely proportional with the drawing speed.

[0040] As noted above disclosed methods may be used to fabricate microparticles or nanoparticles. The particle size as disclosed herein may be tuned by adjusting the tapering parameters, and the physical process described here hence offers an unconventional nonlithographic, top-down approach to fabricating micro and nano-structures using nontraditional materials combinations. To demonstrate control over particle size, the Inventor produced core particles at three different sizes, 5, 2, and 1 pm, where particle size was tuned by varying the tapering speed.

[0041] There are unique features of the disclosed fiber tapering based particle fabrication approach. First, it is amenable to a wide range of materials. Demonstrations have included chalcogenide glasses, low-melting-temperature metals, polymers. Secondly, since tire process can start from a macroscopic rod that is drawn into a fiber, particles of complex structure may be obtained through preparing the rod with the prescribed structure. Thirdly, although the process described herein is generally not efficient in producing particles in terms of volume conversion, the efficiency may be increased by using multi-core fibers where three different cores, all of which can undergone breakup. One may further increase the number of cores until they become hydrodynamically coupled during tapering and the assumption of an unbound cladding breaks down, a limit which has not been investigated heretofore.

[0042] As disclosed above, the size of particles that may be fabricated using disclosed methods extends over a very wide range, such as extending from 1 mm down to approximately 5 nm. The particles can be highly spherical particles. [0Q43] Moreover, the same procedure may be used with a wide variety of materials. The Inventor demonstrated the above- described process with a polymer core. The Inventor observed the same particle generation phenomena occurred with polymer cores that occurred with glass cores. Therefore, disclosed fiber tapering processes can also be used to fabricate micro- and nano-particles of polymers.

[0044] Since disclosed fiber tapering processes are top-down approaches that starts from a structure at the macroscopic scale, the shape of the cylinder of the material can be selected that is desire to break up before the first fiber drawing step. For example, as described above, two hemispheres of different materials can be used. The result is "Janusparticles", which are particles formed of two hemispheres of different core materials. The process may also be extended to multiple sectors of a cylinder to form spherical particles with a sophisticated sub-structure.

[0045] Disclosed embodiments include TFD-based methods to form high-density macroscopic arrays of well-ordered nanowires that can range from about 5 nm to 1 mm. A centimeter-scale macroscopic cylindrical preform containing the nanowire material in the core encased in a polymer scaffold cladding was thermally drawn in the viscous state to a fiber. By cascading several iterations of the TFD process, continuous reduction of the diameter of an amorphous semiconducting chalcogenide glass was demonstrated. Starting from a 10-mm-diameter rod thermally drawing was used to generate hundreds of meters of continuous sub-5 · n -diameter nanowires. Using this approach macroscopic lengths of highdensity, well-ordered, globally oriented nanowire arrays can be produced.

[0046] Experimental results are provided below described relative to FIGs. 4A-6D which demonstrate core periodicity following disclosed processing applied to a fiber preform including a large number of glass cores encased in a polymer cladding. In the axial (length; drawing) direction the resulting particles are ordered since die instability growth is dominated by a single wavelength. In the transverse dimensions particle order is imposed upon the cores during the stacking process to form the preform.

[0047] FIGs. 4A and 4B are scanned SEM micrograph of 27,000 200-nm-diameter intact glass cores exposed from a 1-mm-outer-diameter fiber cross section after dissolving the polymer cladding. G represents glass, A¾Se3, and P the polymer PES. Periodicity of the glass in tire transverse directions is demonstrated.

[0048] FIG. 5 is a scanned high-magnification SEM micrograph of a portion of the fiber core shown in FIGs. 4A and 4B. The stacked fibers in the preform were found to produce a hexagonal lattice (see dashed lines). At each lattice site 80 200-nm glass cores are located as shown in the inset.

[0049] FIGs. 6A-D are scanned SEMs of well-ordered, three-dimensional particle emulsion held in the polymer cladding. FIG. 6 A is a scanned SEM micrograph of a 1-mmdiameter fiber cross section containing 80 7-pm-diameter cores. FIG. 6B is a highermagnification scanned SEM micrograph of the 80 cores, G=As2Se3 and P-PES. FIGs. 6C and 6D are scanned transmission optical micrographs of the fiber side view before and after breakup (via global heating), respectively, showing the resulting spatial distribution of particles held immobilized in the cladding (scaffold) is well-ordered in all 3 dimensions.

[0050] While various disclosed embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Numerous changes to the subject matter disclosed herein can be made in accordance with this Disclosure without departing from the spirit or scope of this Disclosure. In addition, while a particular feature may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application.

[0051] Thus, the breadth and scope of the subject matter provided in (Iris Disclosure should not be limited by any of the above explicitly described embodiments. Rather, the scope of this Disclosure should be defined in accordance with the following claims and their equivalents.

[0052] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms "a," "an," and "the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, to the extent that the terms "including," "includes," "having," "has," "with," or variants thereof are used in either the detailed description and/or

Claims (25)

225937/2 Claims

1. A fiber comprising: a cladding material disposed along a fiber axis length; and a plurality of spherical particles disposed as a sequence along at least a portion of the fiber length and comprising a spherical particle material that is embedded in and different than the fiber cladding material.

2. The fiber of claim 1 wherein the spherical particles are spaced in an orderly periodic sequence.

3. The fiber of claim 1 wherein the spherical particles are characterized by a diameter that is less than 1 mm.

4. The fiber of claim 1 wherein the fiber cladding material and the spherical particle material are characterized by softening temperatures that are sufficiently similar to allow for the cladding and particle materials to be co-drawn from a common fiber preform.

5. The fiber of claim 1 wherein the fiber cladding material comprises a polymer material.

6. The fiber of claim 5 wherein the fiber cladding material comprises polyether sulfone.

7. The fiber of claim 1 wherein the spherical particle material comprises an electrically semiconducting material.

8. The fiber of claim 7 wherein the spherical particle material comprises a chalcogenide glass.

9. The fiber of claim 8 wherein the spherical particle material comprises As2Se3.

10. The fiber of claim 1 wherein the spherical particle material comprises a metal. 225937/2

11. The fiber of claim 1 wherein each spherical particle includes a first hemisphere comprising a first material and a second hemisphere comprising a second material different from the first material.

12. The fiber of claim 1 wherein the sequence of spherical particles comprises a plurality of sequences, each sequence including a plurality of spherical particles that are disposed along at least a portion of the fiber length and comprising a spherical particle material that is embedded in and different than the fiber cladding material and separated from other sequences of spherical particles by the fiber cladding material.

13. The fiber of claim 1 wherein the cladding material and the spherical particle material comprise distinct polymer materials.

14. An embedded particle arrangement, comprising: a multi-material fiber having a length that is greater than one hundred times cross sectional area of the fiber, said multi-material fiber including: a cladding material providing a continuous phase for said multi-material fiber, and a plurality of particles, along at least a portion of said fiber length, embedded in the cladding material, wherein the plurality of particles are separated from one another, and have a median size between 5 nm and 1 mm.

15. The embedded particle arrangement of claim 14, wherein the cladding material comprises a thermoplastic polymer.

16. The embedded particle arrangement of claim 14, wherein the plurality of particles is arranged in a three dimensional distribution of particles.

17. The embedded particle arrangement of claim 14, wherein the particles include a particle first hemisphere comprising a first material and a second hemisphere comprising a second material different from the first material.

18. The embedded particle arrangement of claim 17, wherein the first material comprises a first glass and the second material comprises a second glass. 225937/2

19. A method of fabricating particles, comprising: providing a multi-material preform having at least one fiber core comprising a first material and an outer first cladding layer, comprising a second material different from the first material, outside the fiber core; thermal fiber drawing the multi-material preform to increase a length of said multi material preform to form an extended multi-material fiber having an extended core, and thermally treating the extended multi-material fiber under conditions that cause a break-up of the extended core to form a plurality of core particles embedded in the outer first cladding layer.

20. The method of claim 19, wherein the thermal fiber drawing comprises a first thermal fiber drawing step and at least a second thermal fiber drawing step, comprising: after the first thermal fiber drawing step, arranging a plurality of multi-material fibers within a second outer cladding layer; and performing a second thermal fiber drawing step on the arranged plurality of multi material fibers.

21. The method of claim 19, wherein a maximum temperature during the thermal fiber drawing is less than a maximum temperature during the thermally treating.

22. The method of claim 19, wherein said first material comprises a chalcogenide glass and said second material comprises a thermoplastic polymer.

23. The method of claim 19, further comprising dissolving the cladding after thermally treating the fiber.

24. The method of claim 19, wherein the at least one core comprises two half cylinders each comprising a different material aligned with respect to one another to provide a cylindrical core.

25. The method of claim 24, wherein the two half cylinders comprise a first glass and a second glass, and wherein the plurality of core particles comprise spherical particles including a first hemisphere comprising the first glass and a second hemisphere comprising the second glass.