title: Dependence of buffer acidity and surfactant chain-length on electro-osmotic mobility in thermoplastic microchannels.
abstract: In this paper, we report the dependence of buffer pH and coating surfactant chain-length on electro-osmotic (EO) mobility in co-polyester microchannels. Thermoplastics co-polyester hydrolyzes to anionic functionality to create electrical double layer on the micro-channel walls. These negatively charged sites are partially or completely screened when long-chain surfactants are added into the buffer. This ancillary technique to modify surface charge polarity to avoid analyte adsorption is known as dynamic coating. We develop a theory to predict the EO mobility tendency on buffer acidity considering the combination of pH-dependent surfactant aggregation and surface dissociation. Our findings of pH-dependent EO mobility in coated channels, using three types of quaternary ammonium surfactants, lauryltrimethyammonium bromide (LTAB), trimethyl (tetradecyl) ammonium bromide (TTAB), and cetyltrimethyammonium bromide (CTAB), agree with our theoretical prediction. We also explain the chain-length dependence of mobility with a collaborative adsorption mechanism of surfactant aggregates.
authors.affiliation: Department of Chemistry and Biochemistry, National Chung Cheng University, 160 San Hsing, Ming-Hsiung, Chia Yi 621, Taiwan. chescw@ccu.edu.tw
authors.forename: Shau-Chun
authors.initials: SC
authors.lastname: Wang
authors.forename: Chia-Yu
authors.initials: CY
authors.lastname: Lee
authors.forename: Hsiao-Ping
authors.initials: HP
authors.lastname: Chen
mesh_terms: D002021:Buffers; D020099:Coated Materials, Biocompatible / Q000032:analysis / Q000737:chemistry*; D003198:Computer Simulation; D004563:Electrochemistry / Q000379:methods*; D006863:Hydrogen-Ion Concentration; D046210:Microfluidic Analytical Techniques / Q000295:instrumentation / Q000379:methods*; D008956:Models, Chemical; D008970:Molecular Weight; D009997:Osmotic Pressure; D010969:Plastics / Q000737:chemistry*; D013329:Structure-Activity Relationship; D013499:Surface Properties; D013501:Surface-Active Agents / Q000032:analysis / Q000737:chemistry*
chemical_list: D002021:Buffers; D020099:Coated Materials, Biocompatible; D010969:Plastics; D013501:Surface-Active Agents