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Pangpaiboon N.,Chulalongkorn University | Traiphol N.,Chulalongkorn University | Promarak V.,Suranaree University of Technology | Traiphol R.,Naresuan University | Traiphol R.,Excellence Center on Intelligent Materials and Systems
Thin Solid Films | Year: 2013

This study introduces a new class of materials as a dewetting inhibitor for polystyrene (PS) ultrathin films. Two types of highly branched aromatic (HBA) molecules are added into PS films with thicknesses of 7 nm and 23 nm. Their concentrations range from 0.75 to 5 wt.%. The films are annealed in vacuum oven at elevated temperatures to accelerate dewetting process. Evolution of the film morphologies is followed by utilizing atomic force microscopy and optical microscopy. Contact angle measurements are used to evaluate interfacial interactions in each system. Dewetting area as a function of annealing time and HBA concentration are calculated. We have found that the presence of only 0.5 wt.% HBA can suppress the dewetting dynamics of PS films. Increasing the HBA concentration from 0.5 to 5 wt.% causes systematic decrease of the dewetting rate. In this system, the HBA molecules behave as physical cross-linking points for PS chains, which lead to the improvement of film stability. The efficiency of HBA as a dewetting inhibitor varies with molecular weight of PS while the change of HBA structure hardly affects the dewetting behaviors. © 2013 Elsevier B.V. All rights reserved.


Chanakul A.,Chulalongkorn University | Traiphol N.,Chulalongkorn University | Faisadcha K.,Chulalongkorn University | Traiphol R.,Naresuan University | Traiphol R.,Excellence Center on Intelligent Materials and Systems
Journal of Colloid and Interface Science | Year: 2014

This contribution presents our continuation work on the color-transition behaviors of polydiacetylene(PDA)/ZnO nanocomposites prepared by using three types of monomers, 5,7-hexadecadiynoic acid (HDDA), 10,12-tricosadiynoic acid (TCDA) and 10,12-pentacosadiynoic acid (PCDA). The color-transition behaviors of these nanocomposites upon exposure to acid and base are investigated by utilizing UV/vis absorption spectroscopy. We have found that these PDA/ZnO nanocomposites exhibit colorimetric response at both low and high pH regions. The addition of acid causes the poly(HDDA)/ZnO, poly(TCDA)/ZnO and poly(PCDA)/ZnO nanocomposites to change color from blue to red at pH. ~. 5, 3.5 and 2, respectively. The color of pure PDA vesicles, on the other hand, is hardly affected at this pH range. At high pH region, the pure poly(TCDA) vesicles change color at pH. ~. 8 while it requires much higher pH to induce color transition of the PDA/ZnO nanocomposites. The mechanism responsible for color transition of the PDA/ZnO nanocomposites is explored by various techniques including infrared spectroscopy, zeta potential analyzer and light scattering. Our result provides a new approach for controlling the colorimetric response to pH of PDA-based materials. © 2013 Elsevier Inc.


Pangpaiboon N.,Chulalongkorn University | Traiphol R.,Naresuan University | Traiphol R.,Excellence Center on Intelligent Materials and Systems | Traiphol N.,Chulalongkorn University
Journal of Coatings Technology Research | Year: 2015

This contribution introduces a new class of materials for improving the stability of polystyrene (PS) ultrathin films. Two types of three-arm polystyrenes (TA-PS) with different arm lengths are added into PS thin films with thicknesses of 7 and 23 nm. Concentration of the TA-PS additives is varied from 0 to 40 wt%. The morphological change of PS films upon annealing above its glass transition temperature is followed by utilizing optical and atomic force microscopy. Our results show that the addition of TA-PS into PS films leads to significant improvement of the film stability. The dewetting rate of PS film containing only 5 wt% of TA-PS is 3 times slower than that of the pure PS film. The increase of TA-PS concentration results in systematic decrease of the dewetting rate. We also observe that the dewetting-suppression efficiency of the TA-PS depends significantly on its arm length. © 2015 American Coatings Association


Traiphol N.,Chulalongkorn University | Faisadcha K.,Chulalongkorn University | Potai R.,Naresuan University | Traiphol R.,Naresuan University | Traiphol R.,Excellence Center on Intelligent Materials and Systems
Journal of Colloid and Interface Science | Year: 2015

An ability to control the thermochromic behaviors of polydiacetylene (PDA)-based materials is very important for their utilization. Recently, our group has developed the PDA/zinc oxide (ZnO) nanocomposites, which exhibit reversible thermochromism (Traiphol et al., 2011). In this study, we present our continuation work demonstrating a rather simple method for fine tuning their color-transition temperature. The PDA/ZnO nanocomposites are prepared by varying photopolymerization time, which in turn affects the length of PDA conjugated backbone. We have found that the increase of photopolymerization time from 1 to 120. min results in systematically decrease of the color-transition temperature from about 85 to 40. °C. These PDA/ZnO nanocomposites still exhibit reversible thermochromism. The PDA/ZnO nanocomposites embedded in polyvinyl alcohol films show two-step color-transition processes, the reversible blue to purple and then irreversible purple to orange. Interestingly, the increase of photopolymerization time causes an increase of the irreversible color-transition temperature. Our method is quite simple and cheap, which can provide a library of PDA-based materials with controllable color-transition temperature. © 2014 Elsevier Inc.


Toommee S.,Chulalongkorn University | Traiphol R.,Naresuan University | Traiphol R.,Excellence Center on Intelligent Materials and Systems | Traiphol N.,Chulalongkorn University
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2015

Polydiacetylene (PDA)-based materials exhibit color transition when subjected to external stimuli, making them attractive for sensing technology. The utilization of PDA-based materials can be largely extended by fabricating in different polymer matrices, which normally involves organic solvents as media. Recently, our group has developed PDA/zinc oxide (ZnO) nanocomposites, exhibiting reversible thermochromism in aqueous medium. In this contribution, we demonstrate that the PDA/ZnO nanocomposite can be dispersed in various organic solvents including 1,2-dichlorobenzene, chlorobenzene, toluene, ethanol, butanol, hexanol, chloroform and tetrahydrofuran. The color of pure PDA changes from blue to red in these solvents while the PDA/ZnO nanocomposite remains blue after 30 days. The color reversibility and color-transition temperature of the PDA/ZnO nanocomposite are hardly affected in these organic solvents compared to the system of aqueous medium. We further demonstrate that the PDA/ZnO nanocomposite can be embedded in common polymer matrices such as poly(styrene), poly(methyl methacrylate), poly(ethylene) and poly(vinyl alcohol) by using a simple mixing process. We have found that color reversibility of the PDA/ZnO nanocomposite depends on property of the polymer matrices and persists up to about 200. °C in some systems. The ability to prepare PDA-based materials in different organic solvents and polymer matrices is very important for their utilization in various applications. © 2015 Elsevier B.V.


Potai R.,Naresuan University | Traiphol R.,Naresuan University | Traiphol R.,Excellence Center on Intelligent Materials and Systems
Journal of Colloid and Interface Science | Year: 2013

This study explores roles of initial solvent on the formation of conjugated polymer nanoparticles (CPNs) and their photophysical properties. Stable aqueous CPN dispersion of poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylvinylene)(MEH-PPV) and regioregular poly(3-octylthiophene)(rr-P3OT) are prepared via reprecipitation technique. This preparation method involves the injection of polymer solution in organic solvents into an excess amount of water. We demonstrate that water solubility of the initial solvent is a major factor dictating mechanism of the CPN formation. Dichloromethane (DCM) and tetrahydrofuran (THF), possessing very different water solubilities, are used as initial solvents in this work. The resultant CPNs exhibit quite different sizes and photophysical properties. The preparation of MEH-PPV nanoparticles from DCM solution provides average size of about 127nm. Their absorption and photoluminescence (PL) spectra shift to higher energy region compared to those of the isolated chain. When the THF solution is used, opposite results are observed. Average size of the nanoparticles decreases to about 40nm. Significant redshift of their absorption and PL spectra is also detected. Detailed data analysis indicates that the individual chain conformation and degree of segmental aggregation within the CPNs are quite different. This leads to drastic discrepancies of their photophysical properties. The use of DCM and THF as initial solvents provides the MEH-PPV nanoparticles with green (λmax=535nm) and red (λmax=590nm) photoemission, respectively. The investigation of rr-P3OT provides consistent results. Our study offers a new and simple route to control size and photophysical properties of CPNs by careful selection of the initial solvents. © 2013 Elsevier Inc.


Potai R.,Naresuan University | Kamphan A.,Naresuan University | Traiphol R.,Naresuan University | Traiphol R.,Excellence Center on Intelligent Materials and Systems
Journal of Polymer Science, Part B: Polymer Physics | Year: 2013

Abstact This study explores the role of segmental solubility of regioregular poly(3-octylthiophene) (rr-P3OT) on chain organization and its photophysical properties. In good solvent chlorobenzene (CRB), rr-P3OT chain adopts an extended conformation, allowing long conjugation length of π-electrons. Cyclohexane is a good solvent for octyl side chain but a poor solvent for the thiophene backbone. The selective segmental interactions of rr-P3OT with this solvent induce conformational change of the polymer. Addition of cyclohexane into the CRB solution leads to chain coiling, which in turn causes significant decrease of the conjugation length. Absorption and photoluminescence spectra of the rr-P3OT in cyclohexane exhibit a blueshift of about 16 nm compared to those of the CRB solution. The change of chain conformation is also detectable by monitoring the variation of quantum yield upon increasing cyclohexane ratio. The quantum yield drops from 0.17 ± 0.01 to 0.11 ± 0.01 when the extended rr-P3OT chain transforms into coiled conformation. Hexane is a nonsolvent for rr-P3OT due to its relatively low solubility parameter. The addition of hexane into rr-P3OT solution in cyclohexane forces dense packing of thiophene rings within the coiled chain. An intrachain aggregation occurs in this system, leading to the appearance of three distinct redshift peaks in absorption spectra and the drastic drop of quantum yield. Correlation between the growth of redshift peaks and the decrease of quantum yield is clearly observed. © 2013 Wiley Periodicals, Inc.


Potai R.,Naresuan University | Kamphan A.,Naresuan University | Traiphol R.,Naresuan University | Traiphol R.,Excellence Center on Intelligent Materials and Systems
Synthetic Metals | Year: 2014

This contribution investigates the aggregation behaviors of regioregular poly(3-octylthiophene) (rr-P3OT) in solvent-nonsolvent systems. The photophysical properties of aggregates in different states are studied by utilizing UV/vis absorption, photoluminescent emission (PL) and photoluminescent excitation (PLE) spectroscopy. The rr-P3OT chains are dispersed in different solvents, including chlorobenzene (CRB) and pyridine (PRD). At this condition, the polymer chains are isolated in CRB or associated in PRD, depending on local polymer-solvent interactions. The polymer chains are forced to densely pack by adding a nonsolvent, ethanol. Ratio of the nonsolvent is systematically increased up to 99% (v/v). The aggregation of rr-P3OT chains results in the growth of distinct redshift peaks in absorption spectra. The measurements of site selective PL and PLE spectra detect the existence of two types of aggregates, non-emissive and emissive species. The formation of these two aggregates depends on local packing of rr-P3OT segments. An early stage of the interchain association results in the non-emissive species. When the chain segments are forced to densely pack within the aggregates, emissive species forms. The change of initial solvents also affects the photophysical properties of aggregates. The aggregates formed in the CRB and PRD systems exhibit rather different absorption patterns.© 2013 Elsevier B.V. All rights reserved.

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