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Effect of Isotacticity of Linear Poly(N-isopropylacrylamide) on its Gelation in Benzyl Alcohol
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.
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Photodissociation dynamics of HN3 at 248 nm: a trajectory surface hopping study
The photodissociation dynamics of hydrazoic acid (HN3) at 248 nm has been studied using a quasi-classical variant of the trajectory surface-hopping (TSH) method in conjunction with Tully’s fewest switches algorithm. Trajectories were integrated on-the-fly at the MRCIS(8,9)/6-31++G(d,p) level of theory. Analysis of our trajectory simulation reveals that N2 ($\tilde{X}$1Σg+) + NH (a 1Δ) as the primary major products contributing ~95% of the overall product formation with N3 ($\tilde{X}$2πg)+ H(2S) as the minor products contributing the rest ~5%. No internal conversion (IC) from the first excited state S1 to the ground state S0 was observed in the photodissociation of HN3 from its first excited singlet state (S1). Intersystem crossing(ISC) from the first excited singlet state S1 to the lowest triplet state T1 was predicted to be inefficient based on the calculated weak spin-orbit interactions between the states.
Synopsis We have studied the photodissociation dynamics of hydrazoic acid (HN3) using the trajectory surface-hopping (TSH) method. Our trajectory simulation reveals that N2 ($\tilde{X}$1Σg+) + NH (a1Δ) as the primary major products contributing ~95% of the overall product formation with N3 ($\tilde{X}$2πg)+ H(2S) as the minor products contributing the rest ~5%. No internal conversion (IC) was observed, and intersystem crossing (ISC) was predicted to be inefficient.
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Journal of Chemical Sciences
Volume 135, 2023
All articles
Continuous Article Publishing mode