CS249833B1 - Electrochemical image-former - Google Patents

Abstract

The electrochemical display contains ionic in the electrolyte 10 to 6 moles. 1 '4. A combination of the use of 1,1 ' salt is preferred. -dimethyl-4,4-bipyridinium in concentration 10 "6 to 1 mol l" 1 as electrochemically active sodium lauryl sulphate as surfactants.

Description

The present invention relates to electrochemical imaging systems.

In recent years, in connection with the development of digital technology and electronics, intensive study of electrochemical / electron-based displays has been studied. electrochromic displays, ECD /. They have some advantages over conventional imaging systems, for example based on liquid crystal, in particular memory behavior and low cost / see Vondrák J, Bludská J.;

Electrochromic displays are essentially cells with a polarized working electrode to which a suitable depolarizer is converted electrochemically. Changes in redox forms result in a change in color around the electrode / often accentuated by the accumulation of colored electrolysis products. Coloring can be maintained and removed by reversing the polarity of the electrode by disconnecting the electrical circuit ·

One of the most frequently considered organic depolarizers are derivatives of the bipyridinium series, so-called. viologeny. Typical representatives are the salts of 1,1'-diheptyl-4,4'-bipyridinium, abbreviated diheptylviologens (HV ² *), or structurally similar 4-benzoylpyridinium derivatives (see, e.g., Bruinink J., Kregting CGA,

Ponjeé J.J .: J. Electrochem · Soc. 124 «1854 (1977); Nobuyuki Yoshiike, Shigeo Kondo, Masakazu Fukai: J-Electrochem. Soc.

127, 1496 (1980)]. These depolarizers are reduced to form poorly soluble color radicals forming a color film on the electrode. E.g. for HV ² *,

HV ² * + e '«HV · *

HV ^e * + X "* HV · * X ** where the anion X ~ is typically Br" respectively, H ₂ POj.

To achieve low surface film solubility, considerably hydrophobic viologens _from, for example, the above-mentioned diheptylviologene or asymmetrically substituted derivatives, e.g., benzylheptylviologene (BHV ²⁺ ), are required (see Barna GG *, Fish JG: J. Electrochem). Soc. 128, 1290 (1981)].

The expansion and use of electrochromic displays with organic depolarisers are mainly prevented by the rapid aging of the excluded films. After accumulation and disconnection of the electrical circuit, the molecules reorganize, during which the initially homogeneous film turns into heterogeneous and polycrystalline agglomerates. This results in a partial loss of film contact with the electrode and the inability to completely erase the color recording. With symmetrically substituted viologens, these changes are often noticeable as early as 10 seconds after the film is formed, and generally can be recorded after one to several minutes. Unsymmetrically substituted viologies have a more aging effect, but they cannot be completely eliminated and difficult to use prevents (see Goddard N.J., Jackson A.C.). and Thomas M.G. J. Blectroanal Chem. 1 $$ ·, 325/1983 / $ Barna G. G., Fish J. G., J. Electrochem. Soc. 128, 1290 (1981)].

These disadvantages are overcome by the invention, characterized in that the electrochemical imager contains a surfactant of 10 < -1 > and 1 < -1 > mol &^lt; ^-1 > in the electrolyte. dimethyl-4,4'-bipyridylium as electrochemically active substance is preferred as the surfactant used laurylsfran sodium concentration of 10 ^"6 to 1 mol.l ^'1.

Surfactants form surface films at the phase interface leading to the accumulation of depolarizers or electrochemical conversion products. The surfactants act as phase electron transfer catalysts and facilitate contact between the film and the electrode. Simultaneously with the use of surfactants, it is possible to employ conventional (hydrophilic) viologene derivatives, for example methylviologene (1,1'-dimethyl-4,4 ⁾ -bipyridinium chloride or perchlorate, W ²⁺ .

- 3 The electrochemical imager has the advantage that color surface films are not subject to recrystallization and aging and the recording can be deleted repeatedly. The display did not show any changes from baseline after <200,000 cycles.

The principle of the invention is evident from the example of a methylviologene titre of an electrochromic imager containing sodium lauryl sulphate.

Example

Methylviologene (perchlorate) was repeatedly recrystallized from water before use. The basic electrolyte was 0.1 mol l ^-1 NaH ₂ PO ₄ (pH 4.45).

The formation and properties of surface films were studied by cyclic voltammetry and electrode polarization by rectangular pulses. The polarization range was -0.3 to -0.8 V (versus SCE). The instruments used were the polarographic analyzer PA 3 (laboratory instruments, Prague) and a universal instrument consisting of a source of triangular and reference voltage. sumatore, potentiostat, current-voltage converter and recorder TZ 4100 / see Lasovský J., Crambal P., Rypka M .: Collect. Czech. Chem. Commun. 49, 2187 (1984)]. The working electrode, saturated calomel electrode and large surface platinum plate as auxiliary electrode were also measured using three-electrode connection. All reported potentials are related to a saturated calomel electrode (SCE). The working electrodes were: glass carbon electrode (gC), porosity 1 to 5% (Radiometer, Copenhagen), shiny platinum electrode, highly conductive SnO ₂ electrode formed by a layer of antimony doped tin oxide deposited on a glass substrate, resistance 10 500 500 µl, / square area and mercury electrode. Prior to measurement, the electrolyte was purged with nitrogen.

Polarization of the electrodes with a negative potential (B = -0.8 V) in a solution of methylviologen and sodium lauryl sulphate produces a homogeneous color film of the MV radical ⁺ containing a surfactant and adhering firmly to the electrode. The following comparison shows the effectiveness of the accumulation. By electrolysis of 0.08 mmol of 1 ”solution on a gC electrode (0.1 mol 1 * ¹ NaH ₂ PO ₄ ), a Faraday charge corresponding to 0.0106 mC cm -1 * is passed through the solution. This value

- 4 is typical of a process driven solely by the diffusion of the depolarizer to the electrode. In the presence of 1.2 mmol of 1 '- * · sodium lauryl sulphate is reached after 15 minutes of deposition of the anodic charge necessary to dissolve the film mC value of 3.54 cm ^"2. The amount of electrochemically converted material is 320 times higher than in pure, surfactant-free solutions, and corresponds to the adsorption of approximately 2.2 × 10 MV ⁰⁺ molecules. when introducing a plausible assumption that the surface electro. If the amount per molecule is 0.5 to 1 nm ² , this amount is equivalent to 100 to 200 monolayer. The results for other electrodes were similar.

The amount of accumulated radical and electrode staining intensity depend primarily on the concentration of sodium lauryl sulphate, methylviologene, and accumulation time. Sodium lauryl sulphate should be used in concentrations to maximize its build-up effect

In larger, surfactant concentrations, micellar structures are formed in the solution which reduce the build-up efficiency. If the optimum concentration range of the surfactant is maintained, it is necessary to eliminate the necessary amount of radical (i.e. an amount corresponding to a charge passage of about 1 mC cm &lt; ^{2 &gt;} / is sufficient to use 1 mmol of 1 &apos; The amount of deposited electroactive material increases with accumulation time. From time dependence, it can be seen that sufficient electroactive material accumulates within the first 2 seconds.

As best we appeared electrolyte composition of 0.1 mol l ^"1 Na ^ PO ^, 1 ^ 1.6 mmol sodium lauryl sulfate and 1 mM 1 ^ 'MV ²⁺ combined with shiny platinum working electrode. This cell was loaded with rectangular pulses with an amplitude of 0.5 V / -0.3 -0.8V versus SCE / with a frequency of 0> 5 to 1 Hz and no changes in its properties and behavior were noted after ₁₀ 5 cycles. The deletion of the anodic pulse recording was very fast, visually assessed as immediate, and no color residue left on the electrode to indicate recrystallization and aging of the film. However, the charge required for anodic dissolution of the color film remained unchanged at all times, which also indicates a perfect erasure of the color record.

- 5 The proposed method offers further advantages over existing processes. An electrolyte containing only 1 mmol of 1% methylviologene solution can be used to form films with sufficient contrast. This concentration is 10 to 100 times lower than in conventional procedures, eg based on diheptylviologen. The implementation of the proposed process is very simple and consists only in adding the surfactant at a suitable concentration to the electrolyte solution.

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It should be emphasized that the accumulation of ionic depolarizers and surfactants in the form of thin films and films is a well-known phenomenon * which can always be recorded when properly combining counter ions / see Lasovský J., Grambal F-, Březina F., Šindelář Z .: Authorial Certificate No. 231 631 of 23-8.84 / Methylviologene may be replaced by other viologene derivatives or generally by other cationic depolarisates. Sodium lauryl sulphate is interchangeable with anionic surfactants such as sodium tetradecylsulfonate, sodium dodecylbenzenesulfonate and the like. Anionic depolarizers such as sulphated organic derivatives may also be used in combination with a cationic surfactant such as cetyltrimethylammonium bromide.

Claims (2)

P S S D O O N E N E Z An electrochemical display _of the first, characterized in that it comprises • the electrolyte ionic surface active agent having a concentration of 1O "6-1 mole 1 \ 2. Electrochemical imaging device according to claim 1, characterized in that it contains, as an electrochemically active substance, a hydrophilic derivative of viologene, for example a salt of 1,1'-dimethyl-4,4'-bipyridinium having a concentration of 10 to 1 mol of 1 'and an anionic a surfactant such as sodium lauryl sulfate.