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Effect of Polymer Concentration on the Structure and Dynamics of Short Poly(N,N-dimethylaminoethyl methacrylate) in Aqueous Solution: A Combined Experimental and Molecular Dynamics Study.
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2019-12-26 , DOI: 10.1021/acs.jpcb.9b08966 Dimitris G Mintis 1 , Marco Dompé 2 , Marleen Kamperman 3 , Vlasis G Mavrantzas 1, 4
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2019-12-26 , DOI: 10.1021/acs.jpcb.9b08966 Dimitris G Mintis 1 , Marco Dompé 2 , Marleen Kamperman 3 , Vlasis G Mavrantzas 1, 4
Affiliation
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A combined experimental and molecular dynamics (MD) study is performed to investigate the effect of polymer concentration on the zero shear rate viscosity η0 of a salt-free aqueous solution of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA), a flexible thermoresponsive weak polyelectrolyte with a bulky 3-methyl-1,1-diphenylpentyl unit as the terminal group. The study is carried out at room temperature (T = 298 K) with relatively short PDMAEMA chains (each containing N = 20 monomers or repeat units) at a fixed degree of ionization (α+ = 100%). For the MD simulations, a thorough validation of several molecular mechanics force fields is first undertaken for assessing their capability to accurately reproduce the experimental observations and established theoretical laws. The generalized Amber force field in combination with the restrained electrostatic potential charge fitting method is eventually adopted. Three characteristic concentration regimes are considered: the dilute (from 5 to 10 wt %), the semidilute (from 10 to 20 wt %), and the concentrated (from 20 to 29 wt %); the latter two are characterized by polymer concentrations cp higher than the characteristic overlap concentration cp*. The structural behavior of the PDMAEMA chains in the solution is assessed by calculating the square root of their mean-square radius of gyration ⟨Rg2⟩0.5, the square root of the average square chain end-to-end distance ⟨Ree2⟩0.5, the ratio ⟨Ree2⟩/⟨Rg2⟩, and the persistence length Lp. It is observed that at low polymer concentrations, PDMAEMA chains adopt a stiffer and slightly extended conformation because of excluded-volume effects (a good solvent is considered in this study) and electrostatic repulsions within the polymer chains. As the polymer concentration increases above 20 wt %, the PDMAEMA chains adopt more flexible conformations, as the excluded-volume effects seize and the charge repulsion within the polymer chains subsides. The effect of total polymer concentration on PDMAEMA chain dynamics in the solution is assessed by calculating the orientational relaxation time τc of the chain, the center-of-mass diffusion coefficient D, and the zero shear rate viscosity η0; the latter is also measured experimentally here and found to be in excellent agreement with the MD predictions.
中文翻译：
聚合物浓度对水溶液中短聚甲基丙烯酸N，N-二甲基氨基乙酯的结构和动力学的影响：结合实验和分子动力学研究。
进行了组合的实验和分子动力学（MD）研究，以研究聚合物浓度对聚（N，N-二甲基氨基乙基甲基丙烯酸甲酯）（PDMAEMA）的无盐水溶液的零剪切速率粘度η0的影响，这是一种灵活的热响应性弱的聚电解质，具有庞大的3-甲基-1,1-二苯基戊基单元作为末端基团。该研究是在室温下（T = 298 K）用相对短的PDMAEMA链（每个链均包含N = 20个单体或重复单元）以固定的电离度（α+ = 100％）进行的。对于MD模拟，首先要对几个分子力学力场进行全面验证，以评估其准确再现实验观察结果和建立理论规律的能力。最终采用广义的琥珀色力场结合约束的静电势电荷拟合方法。考虑了三种特征性的浓缩方案：稀释（5至10 wt％），半稀释（10至20 wt％）和浓缩（20至29 wt％）；后两个特征在于聚合物浓度cp高于特征重叠浓度cp *。PDMAEMA链在溶液中的结构行为通过计算它们的平均回转半径的平方根⟨Rg2⟩0.5，即平均方链端到端距离⟨Ree2⟩0.5的平方根来评估。比率⟨Ree2⟩/⟨Rg2⟩和持续长度Lp。据观察，在低聚合物浓度下，由于排除体积效应（本研究中考虑了良好的溶剂）和聚合物链内的静电排斥，PDMAEMA链采用了较硬且略微扩展的构象。当聚合物浓度增加到20 wt％以上时，PDMAEMA链会采用更灵活的构象，因为排他体积效应会起作用，并且聚合物链内的电荷排斥作用会减弱。总聚合物浓度对溶液中PDMAEMA链动力学的影响通过计算链的取向弛豫时间τc，质心扩散系数D和零剪切速率粘度η0来评估。后者也在此处进行了实验测量，发现与MD预测非常吻合。
更新日期：2019-12-27
中文翻译：
聚合物浓度对水溶液中短聚甲基丙烯酸N，N-二甲基氨基乙酯的结构和动力学的影响：结合实验和分子动力学研究。
进行了组合的实验和分子动力学（MD）研究，以研究聚合物浓度对聚（N，N-二甲基氨基乙基甲基丙烯酸甲酯）（PDMAEMA）的无盐水溶液的零剪切速率粘度η0的影响，这是一种灵活的热响应性弱的聚电解质，具有庞大的3-甲基-1,1-二苯基戊基单元作为末端基团。该研究是在室温下（T = 298 K）用相对短的PDMAEMA链（每个链均包含N = 20个单体或重复单元）以固定的电离度（α+ = 100％）进行的。对于MD模拟，首先要对几个分子力学力场进行全面验证，以评估其准确再现实验观察结果和建立理论规律的能力。最终采用广义的琥珀色力场结合约束的静电势电荷拟合方法。考虑了三种特征性的浓缩方案：稀释（5至10 wt％），半稀释（10至20 wt％）和浓缩（20至29 wt％）；后两个特征在于聚合物浓度cp高于特征重叠浓度cp *。PDMAEMA链在溶液中的结构行为通过计算它们的平均回转半径的平方根⟨Rg2⟩0.5，即平均方链端到端距离⟨Ree2⟩0.5的平方根来评估。比率⟨Ree2⟩/⟨Rg2⟩和持续长度Lp。据观察，在低聚合物浓度下，由于排除体积效应（本研究中考虑了良好的溶剂）和聚合物链内的静电排斥，PDMAEMA链采用了较硬且略微扩展的构象。当聚合物浓度增加到20 wt％以上时，PDMAEMA链会采用更灵活的构象，因为排他体积效应会起作用，并且聚合物链内的电荷排斥作用会减弱。总聚合物浓度对溶液中PDMAEMA链动力学的影响通过计算链的取向弛豫时间τc，质心扩散系数D和零剪切速率粘度η0来评估。后者也在此处进行了实验测量，发现与MD预测非常吻合。
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