JPH0374435A - Polar ultrathin film - Google Patents

Abstract

PURPOSE:To obtain the subject stable ultrathin film, molecularly polarized therein and excellent in piezoelectric, pyroelectric effects, etc., by forming monomolecular films using a compound in which a specific functional part is introduced into at least either of hydrophobic groups in two kinds of specified compounds having the hydrophobic groups and alternately cumulating the formed monomolecular films. CONSTITUTION:The objective ultrathin film obtained by introducing a functional part having dipole moment into at least either of hydrophobic groups in (A) a compound [e.g. expressed by the formula R<1>COOH (R<1> is long-chain aliphatic, alicyclic or aromatic hydrophobic group)] having acidic group and the hydrophobic group and (B) a compound [e.g. expressed by the formula R<2>NH2 (R<2> is same as R<1>)] having basic group and the hydrophobic group, using the resultant compound expressed by the formula, etc., forming monomolecular films according to the Langmuir-Blodgett(LB) method utilizing acid-base bonds and alternately cumulating the formed monomolecular films.

Description

[Detailed Description of the Invention] [Summary] Regarding a novel polar ultra-thin film, a polar ultra-thin LB film with stable molecular polarization within the film and excellent piezoelectric effect, pyroelectric effect, and nonlinear optical properties is produced. For the purpose of this, a compound (i) having an acidic group and a hydrophobic group and a compound (ii) having a basic group and a hydrophobic group are combined using the Langmuir-Blodgett (LB) method using an acid-base bond. The polar thin film is formed by using a compound in which a functional moiety having a dipole moment is introduced into at least one of the hydrophobic groups so that the polarities after accumulation do not cancel each other out. Apply a film and add 1tc.

[Industrial application field]

The present invention relates to a novel polar ultra-thin film. This polar ultra-thin film is stable and has piezoelectric, pyroelectric, and nonlinear optical properties.

[Prior Art] LB (Langmuir-Prodgett) membrane is a method in which amphipathic molecules (such as linear saturated fatty acids) are spread on the water surface by a method called the Langmuir-Prodgett (LB) method. It is an organic ultra-thin film that is produced by compressing and forming a monomolecular film onto a substrate layer by layer (accumulating), and its typical production process is as shown in FIG.

That is, as shown in FIGS. 1(a) to 1(f), water 2 is placed in a suitable tank 1, and amphipathic molecules 3 are spread on the water surface to form a monomolecular film. In this tank 1, a substrate 4 such as a glass plate is arranged so that it can be moved up and down, and a floating plate (compression plate) 5 is arranged so that it can be moved horizontally by means of a pulley 6 and a weight 7, for example. A specific method for producing an LB film is to first apply appropriate pressure using a floating plate 5 to a monomolecular film of amphiphilic molecules 3 spread on the water surface (a).
, lower the board 4). Next, as the group t7i 4 is pulled up, a monomolecular film forms on the surface of the substrate 4 (C), after the substrate is pulled up, it is dried (d), and the substrate is lowered again (e).
. By repeating this operation, a cumulative film 8 can be obtained on the substrate 4 (f).

LBII obtained in the second manner has the following characteristics.

- Film thickness can be controlled on the order of molecular length, making it possible to produce uniform, ultra-thin films with large areas.

■Because molecules are aligned in the same layer facing the same direction, the resulting film has a highly ordered structure.

■ Films can be formed at room temperature and pressure.

One of the methods for producing the above-mentioned durable LBII is hetero-accumulation. Since the LB film stacks molecules one layer at a time on a substrate, an ordered organic superlattice can be formed by alternately accumulating different types of molecules (heteroaccumulation). Currently, many studies are being conducted to produce LB films based on intermolecular interactions and to develop new properties. Among these, polar LB films, which have macropolarization in the film by hetero-accumulating molecules with different dipole moments, have piezoelectric, pyroelectric, and nonlinear optical properties, so research toward their practical application is required. is being actively carried out.

[Problem to be solved by the invention]

When a film having a polar structure is produced by the LB method as described above, molecules in the LB film heterogeneously accumulated on a substrate are arranged as schematically shown in FIG. 2 within the film. Polarization corresponding to the difference in the dipole moments of molecules A and B appears in this film, but in this molecular arrangement, the repulsion between molecules is strong, so the film is unstable, and the molecules reverse over time.
Polarization in the entire film is lost. Therefore, in order to suppress such molecular reversal and create a stable polarized film, it is necessary to use highly crystalline molecules or polymerizable molecules to polymerize in-plane. Methods such as doing this have been taken.

Attempts have also been made to stabilize the membrane to some extent by utilizing intermolecular interactions.

However, at present, it has not yet been possible to obtain a stable polarized film that can be put to practical use.

Therefore, the present invention aims to solve the problems of the prior art described above and to produce a polar ultra-thin LBIII that is stable and has excellent piezoelectric effect, pyroelectric effect, and nonlinear optical properties with molecular polarization within the film. purpose.

[Means for Solving the Problems] The polar ultra-thin film according to the present invention comprises a compound (i) having an acidic group and a hydrophobic group and a compound (ii) having a basic group and a hydrophobic group. - In a polar thin film that is alternately accumulated by Lang's own blog (1, B) method using base bonds, the polarities of at least one of the hydrophobic groups after accumulation do not cancel each other out. like,
The bottom film is made of a compound into which a functional moiety with a dipole moment is introduced.

Specific examples of the compounds (i) and (ii) include formulas RICOOH and R''NHz (wherein R1
and R1 are each independently represented by, for example, a long-chain aliphatic group having 16 to 22 carbon atoms, an alicyclic group having 6 to 18 carbon atoms, or an aromatic hydrophobic group having 6 to 18 carbon atoms. The following compounds can be mentioned.

For example, as shown in FIG. 3, if molecules having a carboxyl group and an amino group at the end of the hydrophilic group of an amphipathic molecule are accumulated on pure water, as shown schematically in FIG.
Acid-base bonds are created between the layers and a stable membrane is constructed. Note that the positive-negative charge pairs formed here impart polarity to the film, and as a result, this LB film comes to exhibit an electroless effect.

According to the present invention, a polar functional group is introduced into the amino group part or the carboxyl group part in FIG. 3, and the membrane is stabilized by acid-base interaction, and the orientation of the functional group is fixed. I can do it. Furthermore, by aligning the polarity direction of the functional group with the polarity direction of the acid-base charge pair, the aim is to achieve higher pyroelectric responsiveness and even higher-order effects such as nonlinear optical effects. .

Specific examples of polar groups that can be introduced into at least one of the compounds (i) and (ii) in producing the LB film according to the present invention include N (CHs)z
, NHZ, Br, F, I, CI, and OH, and electron-withdrawing groups such as No, , ON, and the like.

For example, the following can be listed as specific examples of No.8 introduced into a compound containing NH8.

When trying to introduce a highly polar functional group It is common to try to insert However, in the former case, the movement of the functional groups is relatively free, so there is a risk that the molecules will not necessarily align in the same direction, and even in the latter case, molecular inversion occurs, making it difficult to maintain large polarization. It is.

On the other hand, in the present invention, as shown in the principle explanatory diagram of FIG. 5, the Y portion of molecule A has a dipole moment, which points in the direction of the arrow. This is the same direction as the charge pair formed by amine-carboxylic acid. Furthermore, since one end of the Y moiety is fixed by a chemical bond and the other end by an acid-base bond, it can exist stably within the membrane against the repulsion of molecules. In this way, large polarization is stably maintained throughout the film, resulting in high piezoelectric properties, pyroelectric properties, nonlinear optical properties, etc. Note that the above functional groups may be introduced to the carboxyl group side, or may be introduced to both the acidic group and the basic group. However, if the polarization becomes too large, the membrane will become unstable, so only the acid-base bond is introduced. It may be difficult to stabilize this situation.

〔Example〕

Hereinafter, the present invention will be explained in more detail according to Examples.

Molecule A and molecule B have the following structures:
: CHs(CHz)tic In OOH molecule A-
N Hz is electron-donating, and -No is electron-withdrawing. Furthermore, the NHC◯ bond of molecule A does not contribute significantly to polarity. Therefore, the dipole moment of molecule A as a whole points in the direction of the arrow. When this molecule A was hetero-accumulated with stearic acid (molecule B), the molecule assumed a state schematically shown in FIG. 6 within the LB membrane, and a stable polarized structure was constructed. That is, molecules A and B are 2.87x10-'
A chloroform solution of M, pure water as the aqueous phase, CaF
FT-IR measurements were performed on a sample of 10 layers of LB film stacked on a substrate and an Ag-deposited substrate.
Absorption derived from NH3'' and COO- was observed, confirming that both molecules form a salt between the layers. Also, the dichroic ratio of the peak indicates that the benzene ring is oriented almost perpendicular to the substrate. It was confirmed that Al-hetero-accumulation film-
When the pyroelectric current was measured with the AI structure, the amount of current increased by about 30% compared to the pyroelectric current value of a simple acid-base structure (stearic acid + stearyl amine), and the contribution of the functional group part was clear. It became.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to obtain a stable polarized ultra-thin LB film with molecular polarization within the film and excellent piezoelectric properties, pyroelectric properties, and nonlinear optical properties, and its practical value. Moreover, in the present invention, by replacing the functional groups with highly functional molecules, highly advanced membrane functions can be expressed. Molecular alignment technology will become increasingly important for the realization of future molecular devices, and the method of the present invention is extremely effective as a means for achieving this goal.

[Brief explanation of drawings]

Figure 1 shows a typical conventional LBl! Fig. 2 is a drawing that schematically shows the molecular arrangement within the hetero-cumulative LB film, and Fig. 3 shows the formation of acid-base pairs within the film. FIG. 4 is a diagram schematically showing how a general functional group is incorporated into an LB film, and FIG. 5 is a diagram illustrating the present invention in detail. , FIG. 6 is a drawing schematically showing the structure of a film obtained in an example of the present invention. l...tank, 2...water, 3...amphiphilic molecule. 4.
··substrate.

Claims (1)

[Claims] 1. Langmuir-Blodgett ( In a polar thin film formed by alternating accumulation by the LB method, a compound is used in which a functional moiety having a dipole moment is introduced into at least one of the hydrophobic groups so that the polarities after accumulation do not cancel each other out. A polar ultra-thin film characterized by being formed by forming a film using 2. The compounds (i) and (ii) each have the formula R
^1COOH and R^2NH_2 (in the formula, R^1 and R
2. The polar ultra-thin film according to item 1, wherein ^2 each independently represents a long-chain aliphatic, alicyclic, or aromatic hydrophobic group.