Smith Grant D, Zhang Ye, Yin Fang, Bedrov Dmitry, Dadmun M D, Huang Zhenyu
Department of Materials Science and Engineering, University of Utah, 122 S. Central Campus Drive, Salt Lake City, Utah 84112, USA.
Langmuir. 2006 Jan 17;22(2):664-75. doi: 10.1021/la051750v.
The irreversible adsorption of telechelic polymer chains from solution and melts onto solid substrates has been studied using the bond fluctuation Monte Carlo model. Complex brush formation kinetics dominated by diffusion of chains to the substrate at short times (diffusion-limited regime or DLR) and by penetration of chains through the maturing brush at longer times (penetration-limited regime or PLR) were observed. During the entire adsorption process, the rate of chain adsorption decreases monotonically with time. In the DLR, characterized by a maximum in the concentration of singly bound chains and a rapidly increasing fraction of doubly bound chains (loops), this decrease is due primarily to the depletion of free chains near the substrate and the formation of concentration gradients of free (nonadsorbed) chains in the bulk solution. The DLR and PLR are separated by an intermediate regime during which the brush becomes dominated by doubly bound chains and both penetration of the maturing brush and diffusion of chains to the brush surface play a role in determining the kinetics of brush growth. The PLR is characterized by steep gradients of free chains within the growing brush and the disappearance of concentration gradients for free chains in the bulk solution. In the PLR, the concentration of singly bound chains is low and decreases slowly while surface coverage and the fraction of doubly bound chains increase slowly. The rates of adsorption of new chains and the formation of loops in the PLR slow dramatically with increasing surface coverage and increasing chain length and less dramatically with decreasing bulk concentration.
利用键涨落蒙特卡罗模型研究了遥爪聚合物链从溶液和熔体到固体基质上的不可逆吸附。观察到了复杂的刷状形成动力学，在短时间内（扩散限制区或DLR）由链向基质的扩散主导，而在较长时间内（渗透限制区或PLR）由链穿过成熟刷的渗透主导。在整个吸附过程中，链吸附速率随时间单调下降。在DLR中，其特征是单键合链的浓度达到最大值，双键合链（环）的比例迅速增加，这种下降主要是由于基质附近自由链的耗尽以及本体溶液中自由（未吸附）链浓度梯度的形成。DLR和PLR之间被一个中间区域隔开，在此期间刷状结构由双键合链主导，成熟刷的渗透和链向刷表面的扩散在决定刷状生长动力学方面都起作用。PLR的特征是生长刷内自由链的陡峭梯度以及本体溶液中自由链浓度梯度的消失。在PLR中，单键合链的浓度较低且下降缓慢，而表面覆盖率和双键合链的比例则缓慢增加。随着表面覆盖率的增加和链长的增加，PLR中新链的吸附速率和环的形成速率急剧减慢，而随着本体浓度的降低，减慢的幅度较小。
