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      https://www.ias.ac.in/article/fulltext/jcsc/128/06/0941-0950

    • Keywords

       

      Linear poly(N-isopropylacrylamide); isotacticity; thermo reversible gelation; benzyl alcohol.

    • Abstract

       

      Thermoreversible gelation of three different isotactic linear poly(N-isopropylacrylamide) (PNIPAM)s having meso dyad (m) values 62, 68 and 81% has been observed in benzyl alcohol. All the gels weretransparent in nature. SEM image of the dried gels showed fibrillar network morphology. Melting temperatureof the gels gradually increased with the increase in the concentration. XRD data of dry polymers and their correspondingdry gels showed shifting in the peak positions. Rheological study showed that stronger gels wereformed with increasing isotacticity of PNIPAM while lower isotactic sample exhibited typical polymer meltrheology. The formation of a plunge in the storage modulus as well as in the viscosity plot at the same frequencyrange indicates the reversible nature of the structure breaking/reformation under frequency sweep. Moreover,the mechanical strength of the gel decreased with increase in temperature. UV-Vis kinetic study also indicatedthe change in the conformation and aggregation of PNIPAM chains during gelation. Molecular modelling calculationshowed that the number of solvent molecules involved in forming gel (polymer-solvent compound)decreased with the increase in the isotacticity of the polymer. Gelation rate of these gels was studied as a functionof temperature, concentration and isotacticity using test-tube tilting method. It increased with the increasein the concentration and isoacticity of the polymer, and with the decrease in the temperature. Critical gelationconcentration of the gel gradually increased with the decrease in the isotacticity and with the increase in thetemperature. All these experimental results indicated that gelation occurs presumably through polymer-solventcompound formation.

    • Author Affiliations

       

      CHANDRA SEKHAR BISWAS1 2 KHEYANATH MITRA1 SHIKHA SINGH1 DINESH K PATEL3 BISWAJIT MAITI1 PRALAY MAITI3 BISWAJIT RAY1 2

      1. Department of Chemistry, Institute of Science, Banaras Hindu University, Varanasi 221 005, India
      2. Nanshan District Key Lab for Biopolymers and Safety Evaluation, College of Materials Science and Engineering and Optoelectronic Engineering Postdoctoral Centre, Shenzhen University, 518060 Shenzhen, China
      3. School of Material Science and Technology, Indian Institute of Technology, Banaras Hindu University, Varanasi 221 005, India
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