Diffusion of mesoscopic probes in aqueous polymer solutions measured by fluorescence recovery after photobleaching
Diffusion of mesoscopic probes in aqueous polymer solutions measured by fluorescence recovery after photobleaching
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DOI：
10.1021/ma0107758
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发表时间：
2002-10-08
期刊：
影响因子：
5.5
通讯作者：
Thomas, JL
中科院分区：
文献类型：
--
作者：
Cheng, Y;Prud'homme, RK;Thomas, JL
采用荧光漂白后恢复法（FRAP）跟踪介观探针（1 nm < R < 20 nm）在聚氧化乙烯（PEO）和瓜尔胶半乳甘露聚糖水溶液中的扩散。我们将“介观”定义为扩散物质的尺寸与聚合物基质溶液中的屏蔽长度具有相同数量级的区域。我们表明，扩散不仅取决于无量纲的长度尺度R/zeta，但也对无量纲的时间尺度上对应的松弛的聚合物网格的“约束释放”与时间的探针物种的运动的长度。使用两种不同的FRAP技术：条纹图漂白和恢复（FPBR）和共聚焦扫描激光显微镜（CSLM）。通过测量具有不同分形维数（d（f））的探针，研究了探针结构对通过聚合物基质扩散的影响：蛋白质和聚苯乙烯乳胶颗粒表现为刚性球体（d（f）= 3）;葡聚糖是具有更扩展构象的轻微支化聚合物（d（f）= 2.3）;树枝状聚合物落在这两者之间，密度首先降低，然后随着世代增加。低代（G 0）和高代（G9-G10）的树枝状聚合物是紧凑的，而中间代（G2-G6）是更多孔的。发现探针扩散是探针分形维的函数：刚性球体在半稀释和浓缩聚合物溶液中的扩散比在自由溶液中具有相同流体动力学尺寸的右旋糖酐分子受到的阻碍更大，缩放方程D/D-0 = exp[-beta（R/zeta）（delta）]对于介观刚性球形探针，与实验结果非常吻合。还讨论了基体聚合物刚度和聚合物分子量的影响。在恒定的屏蔽长度ζ（即，恒定的聚合物浓度）不同分子量的聚合物来证明介观探针扩散的区域，其与基质聚合物分子量无关。从使用柔性PEO和更刚性的瓜尔胶作为基质聚合物的测量中示出了扩散率对基质聚合物持续长度l（p）与筛目尺寸ζ的比率的依赖性。在相同的网格尺寸下，通过更刚性基质的扩散相对于通过更柔性网格的扩散受到阻碍;随着浓度增加和网格尺寸减小，这种影响变得更加明显。
Fluorescence recovery after photobleaching (FRAP) has been used to follow the diffusion of mesoscopic probes (1 nm < R < 20 nm) in aqueous poly(ethylene oxide) (PEO) and guar galactomannan solutions. We define "mesoscopic" as the regime for which the size of the diffusing species is of the same order as the screening length in the polymer matrix solution. We show that diffusion depends not only on the dimensionless length scale R/zeta but also on the dimensionless time scale corresponding to the relaxation of the polymer mesh by "constraint release" vs the time for motion of the probe species over the length. Two different FRAP techniques were used: fringe pattern bleaching and recovery (FPBR) and confocal scanning laser microscopy (CSLM). The effect of probe structure on diffusion through polymer matrices was investigated by measurements on probes with differing fractal dimensions (d(f)): proteins and polystyrene latex particles behave as rigid spheres (d(f) = 3); dextrans are slightly branched polymers with a more expanded conformation (d(f) = 2.3); dendrimers fall between these two with a density first decreasing and then increasing with generation. Dendrimers at low generations (GO) and high generations (G9-G10) are compact, while the intermediate generations (G2-G6) are more porous. Probe diffusion was found to be a function of the fractal dimension of the probe: the diffusion of rigid spheres was shown to be more hindered in semidilute and concentrated polymer solutions than dextran molecules with the same hydrodynamic size in free solution, The scaling equation D/D-0 = exp[-beta(R/zeta)(delta)] fit the experimental results well for mesoscopic, rigid spherical probes. The effects of matrix polymer stiffness and polymer molecular weight were also addressed. At constant screening length zeta (i.e., constant polymer concentration) polymers of different molecular weights are used to demonstrate the region of mesoscopic probe diffusion that is independent of the matrix polymer molecular weight, The dependence of diffusivity on the ratio of the matrix polymer persistence length l(p) to the mesh size zeta was shown from measurements using the flexible PEO and more rigid guar as matrix polymers. At equal mesh size, diffusion through the more rigid matrix is hindered relative to that through the more flexible mesh; this effect becomes more pronounced as concentration increases and mesh size decreases.