Ester Films Research Articles

Kinetic absorption of vapors of alkyl acetates C1-C4 and diethyl ether on thin films of modified piezoelectric quartz resonators

Sorption of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, and diethyl ether on thin films of esters: poly(ethylene glycol) sebacate and phthalate, dinonyl phthalate, tween-40, pentaerythritol tetrabenzoate, triphenyl phosphate, Triton X-305, and stearic acid was studied. The mass of sorbent films was optimized, the sensitivity and selectivity of modifiers toward analytes was evaluated, and the time of maximum sorption was determined.

Expedient, accurate methods for the determination of the degree of substitution of cellulose carboxylic esters: Application of UV–vis spectroscopy (dye solvatochromism) and FTIR

Two techniques, namely UV–vis- and FTIR spectroscopy, have been employed in order to calculate the degree of substitution (DS) of cellulose carboxylic esters, including acetates, CAs, butyrates, CBs, and hexanoates, CHs. Regarding UV–vis spectroscopy, we have employed a novel approach, based on measuring the dependence of λ max of the intra-molecular charge-transfer bands of polarity probes adsorbed on DS of the ester films (solvatochromism). Additionally, we have revisited the use of FTIR for DS determination. Several methods have been used in order to plot Beer's law graph, namely: Absorption of KBr pellets, pre-coated with CA; reflectance (DRIFTS) of CAs-KBr solid–solid mixtures with, or without the use of 1,4-dicyanobenzene as an internal reference; reflectance of KBr powder pre-coated with CA. The methods indicated are simple, fast, and accurate, requiring much less ester than the titration method. The probe method is independent of the experimental variables examined.

Investigation of the effects of substrate annealing on the properties of polymer blends

In this manuscript, we investigated the effect of substrate annealing prior to the deposition of the active layer on the morphological, structural and opto-electrical properties of two variations of organic polymer blends of poly (3-hexylthiophene):C 60 fullerene and poly (3-hexylthiophene):[6,6]-phenyl C 61 butyric acid methyl ester films using atomic force microscopy, field emission scanning microscopy, x-ray diffraction and Hall effect measurements. P3HT films deposited on pre-annealed substrates exhibit an enhancement in the crystallization, and an increase in the electrical conductivity and Hall mobility of p-type P3HT. The microscopic morphology reveals self-assembled fibrillar structures due to the suppressed growth of fullerenes clusters induced by the controlled evaporation rate of the solvent. It is proposed that pre-substrate annealing controls the crystallization of P3HT, the phase separation and diffusion of the acceptor material (C 60 or PCBM).

All-spin-coating vacuum-free processed semi-transparent inverted polymer solar cells with PEDOT:PSS anode and PAH-D interfacial layer

Semi-transparent inverted polymer solar cells (PSCs) were fabricated by all-spin-coating vacuum-free process. An interfacial layer of poly(allylamine hydrochloride) and dextran (PAH-D) was introduced to modify the surface wettability of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methyl ester (PCBM) film for depositing aqueous-solution-processed poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) (CLEVIOS™ PH500) (PH500) anode as well as enhancing the adhesion and bonding strength between the active layer (P3HT:PCBM) and conducting polymer electrode (PH500). The photovoltaic performance of the semi-transparent PSCs under top and bottom illumination was investigated and the highest PCE of about 1.86% was achieved under simulated AM 1.5 illumination (100 mW/cm 2) from the bottom side with a reflective white paper back side. The semi-transparent Cell A have the potential for use as energy-generating color window glasses as well as the subcell of tandem solar cells. The all-spin-coating vacuum-free processing provides a possibility of high-throughput all-solution-processed fabrication of PSCs by roll-to-roll processing.

Control of Thin Liquid Film Morphology During Solvent-Assisted Film Deposition

Liquid films of different silicate esters were deposited from volatile solvents on hydroxylated and hydrogen-passivated silicon surfaces. We show that adsorption of silicate ester molecules and the resulting structural morphology of the liquid films not only are determined by attractive van der Waals forces with contributions from electrostatic interactions between the silicone ester moieties and oxide surface sites but also can be tuned by modifying the substrate surface or by changing the liquid-solvent interactions. Our results also show the importance of the conformational properties of liquid molecules and their rearrangements at the liquid/solid interface for controlled solvent-assisted film deposition.

Transient Absorption Studies of Bimolecular Recombination Dynamics in Polythiophene/Fullerene Blend Films

Bimolecular recombination, an important loss mechanism in organic solar cells, has been investigated using transient absorption spectroscopy for poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) films and analogues of these components. Data are analyzed as a function of blend composition, postdeposition thermal annealing, and excitation density. Comparison of transient spectra for P3HT:PCBM films with analogous films employing P3HS and PC70BM allows the assignment of the photoinduced absorption features. These decay dynamics are analyzed on the nanosecond to millisecond time scales and are shown to be in excellent agreement with a bimolecular recombination model in the presence of an exponential distribution of localized (trap) states. Thermal annealing results in an acceleration of these decay dynamics, which is assigned to a reduction in the depth of the trap states and correlated with an increase in film crystallinity. The decay dynamics are analyzed to obtain an effective recombination coefficient that is charge density dependent at low polaron densities, but becomes independent of charge density at high charge carrier densities (>1018 cm−3). This transition is assigned to trap filling, with the recombination coefficient measured at high charge density (k = 3 × 10−12 cm3 s−1) corresponding to the trap-free limit. From transient spectroscopic behavior we estimate the density of intraband trap states in unannealed P3HT:PCBM blend films to be ∼7 × 1017 cm−3.

Surface-Segregated Monolayers: A New Type of Ordered Monolayer for Surface Modification of Organic Semiconductors

We report a new type of ordered monolayer for the surface modification of organic semiconductors. Fullerene derivatives with fluorocarbon chains ([6,6]-phenyl-C(61)-buryric acid 1H,1H-perfluoro-1-alkyl ester or FC(n)) spontaneously segregated as a monolayer on the surface of a [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) film during a spin-coating process from the mixture solutions, as confirmed by X-ray photoelectron spectroscopy (XPS). Ultraviolet photoelectron spectroscopy (UPS) showed the shift of ionization potentials (IPs) depending on the fluorocarbon chain length, indicating the formation of surface dipole moments. Surface-sensitive vibrational spectroscopy, sum frequency generation (SFG) revealed the ordered molecular orientations of the C(60) moiety in the surface FC(n) layers. The intensity of the SFG signals from FC(n) on the surface showed a clear odd-even effect when the length of the fluorocarbon chain was changed. This new concept of the surface-segregated monolayer provides a facile and versatile approach to modifying the surface of organic semiconductors and is applicable to various organic optoelectronic devices.

Stability and interface properties of thin cellulose ester films adsorbed from acetone and ethyl acetate solutions

Stability and interface properties of cellulose acetate propionate (CAP) and cellulose acetate butyrate (CAB) films adsorbed from acetone or ethyl acetate onto Si wafers have been investigated by means of contact angle measurements and atomic force microscopy (AFM). Surface energy ( γ S total ) values determined for CAP adsorbed from acetone are larger than those from ethyl acetate. In the case of CAB films adsorbed from ethyl acetate and acetone were similar. Dewetting was observed by AFM only for CAP films prepared from ethyl acetate. Positive values of effective Hamaker constant ( A eff ) were found only for CAP prepared from ethyl acetate, corroborating with dewetting phenomena observed by AFM. On the contrary, negative values of A eff were determined for CAP and CAB prepared from acetone and for CAB prepared from ethyl acetate, corroborating with experimental observations. Sum frequency generation (SFG) vibrational spectra indicated that CAP and CAB films prepared from ethyl acetate present more alkyl groups oriented perpendicularly to the polymer–air interface than those films prepared from acetone. Such preferential orientation corroborates with macroscopic contact angle measurements. Moreover, SFG spectra showed that acetone binds strongly to Si wafers, creating a new surface for CAP and CAB films.

Preparation and physical properties of chitin fatty acids esters

Trifluoroacetic anhydride is an effective promoter for the preparation of chitin single- and mixed-acid esters. Complete dissolution is achieved within 30 min when powdered chitin is heated at 70 °C in a mixed solution of carboxylic acid(s) and trifluoroacetic anhydride. Chitin esters prepared are chitin acetate, chitin butyrate, chitin hexanoate and chitin octanoate, chitin co-acetate/butyrate, chitin co-acetate/hexanoate, chitin co-acetate/octanoate, chitin co-acetate/palmitate, each from a solution of the respective reactants. The products have degrees of O-acyl substitution in a range of DS 1–2 depending on the nature of acyl group, as analyzed by gas–liquid and high-pressure liquid chromatography. Acetic acid as a mutual component for the mixed-acid esters increases the total degree of substitution, and the acetyl substitution is close to the relative distribution in the reaction mixture for chitin co-acetate/butyrate. It is favored over hexanoate, octanoate, and palmitate. The parent molecules, as calculated by the composition of the chitin esters and their molecular weights by light-scattering spectroscopy, are 30 kDa for the smallest and 150–151 kDa for the largest. Films of these chitin derivatives when cast from solution are strong and flexible with limited extensibility. By dynamic mechanical analysis of the ester film, it was found that both the glass transition temperature ( T g) and the tensile modulus ( E′ at 25 °C) are highest for chitin acetate (218 °C and 5.8 GPa), and lowest for chitin octanoate (182 °C and 1.5 GPa). For the other esters, these values lie between the above-cited values, where the T g and the E′ decrease with an increase in the chain length of the acyl constituent.

1,8-octanedithiol as a processing additive for bulk heterojunction materials: Enhanced photoconductive response

We present measurements of steady state and transient (τ<70ps) photoconductivity of the low bandgap polymer poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] mixed with [6,6]-phenyl C71-butyric acid methyl ester films processed with and without the 1,8-octanedithiol additive. The data demonstrate enhanced photoconductive response in the bulk heterojunction material processed with the additive. The increase results primarily from enhanced carrier mobility and to a lesser extent from a more efficient photogeneration of mobile carriers and longer mobile carrier lifetimes. The enhanced photoresponse is consistent with the increase in power conversion efficiency obtained from solar cells in which the bulk heterojunction film is processed using 1,8-octanedithiol.

Efficacy of TiOx optical spacer in bulk-heterojunction solar cells processed with 1,8-octanedithiol

The efficacy of TiOx as an optical spacer in bulk-heterojunction (BHJ) solar cells made from regioregular poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester films processed with 1,8-octanedithiol is investigated. The results indicate that the enhanced efficiency resulting from the TiOx optical spacer is anticorrelated to the concentration of the processing additive. The use of the processing additive induces surface roughness on the BHJ film and thereby diminishes the efficacy of the optical spacer. Solar cells fabricated with both the optical spacer and 1,8-octanedithiol yield efficiencies that are superior to those with either process alone.

Nanoscale Charge Transport and Internal Structure of Bulk Heterojunction Conjugated Polymer/Fullerene Solar Cells by Scanning Probe Microscopy

Tapping mode atomic force microscopy (AFM) was used to probe the surface and internal structures of bulk heterojunction poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) films. AFM images obtained from the surface of the P3HT:PCBM film and from the cross section reveal for the first time the nanoscale three-dimensional P3HT and PCBM networks. Two different measurement modes of conducting atomic force microscopy (C-AFM) were used to study the nanoscale charge transport in P3HT:PCBM films. In C-AFM, the local current map at a constant bias and the surface topography are obtained simultaneously. Hole and electron current images can be used to determine the composition of the phase segregation domains. Alternatively, local current−voltage curves can be measured that can be used to calculate charge carrier mobilities. Hole current images and mobilities were obtained using Pt-coated silicon probes, whereas Mg-coated silicon probes were used to measure nanoscale electron mobilitie...

Characteristics of thin cellulose ester films spin-coated from acetone and ethyl acetate solutions

Spin-coated films of cellulose acetate (CA), cellulose acetate propionate (CAP), cellulose acetate butyrate (CAB) and carboxymethylcellulose acetate butyrate (CMCAB) have been characterized by ellipsometry, atomic force microscopy (AFM) and contact angle measurements. The films were spin-coated onto silicon wafers, a polar surface. Mean thickness values were determined by means of ellipsometry and AFM as a function of polymer concentration in solutions prepared either in acetone or in ethyl acetate (EA), both are good solvents for the cellulose esters. The results were discussed in the light of solvent evaporation rate and interaction energy between substrate and solvent. The effects of annealing and type of cellulose ester on film thickness, film morphology, surface roughness and surface wettability were also investigated.

Hyaluronic acid ester in myringoplasty

To investigate the use of a new technique to close persistent tympanic membrane perforations under general anaesthesia, in patients in whom this has previously been considered impractical. Twenty patients aged 50 years and over were recruited. All had a persistent, symptomatic tympanic membrane perforation in at least one ear. Pre-operatively, an audiogram was performed and the tympanic membrane was assessed in order to establish the site and size of the perforation. Under general anaesthesia, the edges of the perforation were freshened and a sheet of Epifilm, trimmed to a size roughly 2 mm larger in diameter than the perforation, was tucked through the perforation. The ear was dressed appropriately. Patients were seen two weeks post-operatively in the out-patients department and reassessed. The study was based at Poole General Hospital, a District General Hospital. Twenty patients were recruited from the out-patients clinics of Poole Hospital ENT department. (1) closure of the perforation, as a percentage of the original size; (2) improvement of hearing, as an average across all frequencies, expressed in dB hearing level; and (3) presence or absence of discharge. Five patients were operated upon and assessed six weeks post-operatively. The Epifilm had dissolved but the perforations remained the same size in all five patients. There were no other adverse effects. Pure tone audiometry at this stage was redundant. The study was subsequently aborted. The authors conclude that repair of tympanic membrane perforations with hyaluronic acid ester films is not to be recommended.

Hydrogen-Bonding-Induced Conformational Change from J to H Aggregate in Novel Highly Fluorescent Liquid-Crystalline Perylenebisimides

A series of highly fluorescent liquid-crystalline perylenebisimide molecules having amide or ester linkage and end-capped by phenyl, monododecyloxy phenyl, or tridodecyloxy phenyl units have been synthesized and fully characterized. The amide-functionalized series self-organized to form H type aggregates regardless of their end-capping in organic solvents like tetrahydrofuran (THF), toluene, and dichloromethane. On the other hand, only the monododecyloxy phenyl end-capped molecule in the ester series showed a tendency to self-organize with a typical J type aggregation in toluene. In both series, the highest aggregation tendency was shown by the one having monododecyloxy phenyl end-capping, with the transition temperature from aggregated to molecularly dissolved species occurring at 60 °C for the amide and 50 °C for the ester molecule. At higher concentrations in toluene, the fluorescence spectra of the monododecyloxy phenyl and tridodecyloxy phenyl terminal-substituted amide derivatives showed the formation of a new peak corresponding to excimer emission at 670 nm. Thin drop cast films of the perylenebisimide ester and amide series gave only excimer emission ∼670 nm upon excitation. Thermal analysis using differential scanning calorimetry (DSC), polarized light microscopy (PLM), and powder X-ray diffraction measurements were utilized to study the liquid-crystalline (LC) characteristics of the molecules. Scanning electron micrograph (SEM) of thin drop-cast samples that were annealed in toluene showed the formation of supramolecular rods several micrometers in length, especially for the amide derivatives. The ester derivative, on the other hand, showed a leaflike morphology thus differentiating it from the amide series, which have both hydrogen bonding and π−π interactions to support self-organization.

Dewetting and surface properties of ultrathin films of cellulose esters

Surface properties of ultrathin films of cellulose esters deposited onto silicon wafers have been investigated by means of contact angle measurements and atomic force microscopy (AFM). Cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB) films adsorbed or spin-coated onto Si wafers were annealed up to one week. Film stability was monitored by AFM. Dewetting has been observed for CA and CAP. Only CAB films with lower degree of esterification presented dewetting, CAB films with high degree of butyrate were stable even after one week annealing. Surface energy of CA, CAP, and CAB was indirectly determined by contact angle measurements using drops of water, formamide and diiodomethane. The surface energy decreased as the size of alkyl ester group or the degree of esterification increased because van der Waals interactions became weaker. Effective Hamaker constant A eff was calculated for CA, CAP, and CAB onto Si wafers in air. Negative values of A eff were found for CA, CAP, and lower butyrate content CAB, which are related to instability and agree with dewetting phenomena observed by AFM. In contrast, a positive A eff was determined for higher butyrate content CAB, corroborating with experimental observations.

Biomedical evaluation of polyvinyl alcohol–gelatin esterified hydrogel for wound dressing

The wound is a biosynthetic environment in which numerous cellular processes are interlinked in the process of repair. Modern dressings are designed to facilitate wound healing rather than just to cover it. Hydrogel dressing can protect injured skin and keep it appropriately moist to speed the healing process by absorbing exudates while maintaining the products of tissue repair, including growth factor and lysosomes, in contact with the wound. The design and development of novel membrane of hydrogels prepared by esterification of polyvinyl alcohol with gelatin were attempted. Contact angle of goat blood was determined. The hydrogel was characterized by hemolysis test and water vapor transmission rate. Diffusion coefficient of salicylic acid (SA) and gatifloxacin, a fourth generation fluoroquinolone, through the membrane was determined. Both the drugs were used as model drug. Methyl tetrazolium dye assay of the membrane was done using L929 fibroblast cell line and mice splenocytes to establish the biocompatibility of the membrane. The equilibrium goat blood-in-air contact angles of measured ester films ranged from 56 to 60 degrees . The hydrogel was found to be hemocompatible and moisture retentive indicating its possible use in moist wound care. The diffusion coefficient of SA and gatifloxacin through the membrane was found to be 1.49 x 10(-5) and 3.97 x 10(-6) cm(2)/s respectively. The membrane was found to be compatible with the L929 fibroblast cell line and mice splenocytes.

Photocurrent generation by benzoporphyrin films prepared by a solution process

Tetrabenzoporphyrin films on indium-tin-oxide electrodes were prepared by continuous spin-coating of indium-tin-oxide electrodes with a soluble precursor, tetrabicyclo[2.2.2]octadiene-fused porphyrin, and subsequent thermal conversion of the precursor to tetrabenzoporphyrin by annealing the modified electrodes. When the tetrabenzoporhyrin-modified indium-tin-oxide working electrode was irradiated in a three-electrode system, using Pt as a counter electrode and Ag / Ag + as a reference electrode in the presence of hexyl viologen as an electron acceptor, a cathodic photocurrent was observed. A double layer structure consisting of tetrabenzoporphyrin and [6,6]-phenyl- C 61 butyric acid methyl ester (PCBM) films and a triple layer structure consisting of tetrabenzoporphyrin; a mixture of tetrabenzoporphyrin and PCBM; and PCBM films were also prepared on indium-tin-oxide electrodes by repeated spin-coating. The incident photon to photocurrent efficiency values of up to 6.8% were obtained for the triple layer structure, in which the mixed layer contained tetrabenzoporphyrin and PCBM molecules in a 7:3 ratio. Action spectra of the triple layer structure showed that visible light from 380 to 700 nm sensitized the system for photocurrent generation.

Ambipolar Field-Effect Transistors Based on Poly(3-hexylthiophene)/Fullerene Derivative Bilayer Films

Field-effect transistors (FETs) based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric methyl ester (PCBM) films have been studied for various structures with metal electrodes on a SiO2/Si substrate. The pressure dependence of transport characteristics in P3HT FET during evacuation was measured. It was found that hole mobility is independent of atmospheric pressure, whereas hole density decreases significantly with evacuation. FET characteristics in various configurations (top and bottom) of contact with Au and Al were examined in P3HT and PCBM films. The results indicate that bottom contact with Au gives better performance for bilayer FETs. Ambipolar transport was observed for the bilayer structure of PCBM (upper)/P3HT (lower)/Au (bottom contact).

Engineering cartilage tissues with the shape of human nasal alar by using chondrocyte macroaggregate—Experiment study in rabbit model

Despite of progresses in tissue engineering based on cell/scaffold strategy, uneven cell distribution as well as tissue formation in the scaffold, limited cell seeding efficiency and inflammatory reaction triggered by the degradation of scaffold remain problems to be resolved. In this study, we proposed a novel cell-macroaggregate cultivation system, and explored a feasible strategy to construct three-dimensional cartilage tissue with shape of human nasal alar by using cell macroaggregate. Isolated chondrocytes was cultured at high density to form a monolayer chondrocyte sheet as well as expanded for seeding on the sheet to produce mechanically operable cell macroaggregate. Chondrocyte macroaggregates were then fabricated into transplants with shape of nasal alar by using Internal support or External scaffold techniques; results of in vivo chondrogenesis were investigated in immunocompetent animal. Chondrocyte macroaggregates presented long survival time and good viability; constructs fabricated using both techniques can develop into tissues with characteristic structure of native cartilage, glycosaminoglycans as well as type II collagen were highly produced in the ECM of engineered cartilages. By placing hyaluronan ester film as Internal support, the predetermined shape of the chondrocyte macroaggregate can be well maintained. In contrast, due to the poor mechanical stability of grafts fabricated in External scaffold group, obvious deformation occurred in harvested specimens. The experiment proved the usefulness of chondrocyte macroaggregate in cartilage regeneration, and provided a new strategy to engineer cartilage with special shape by using cell macroaggregate/biodegradable support.