Effective charges along the melting line of colloidal crystals.
Effective charges along the melting line of colloidal crystals.
复制标题
沿胶体晶体熔线的有效电荷。
DOI：
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发表时间：
2006
影响因子：
4.4
通讯作者：
T. Palberg
中科院分区：
文献类型：
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作者：
L. Shapran;H. Schöpe;T. Palberg
带电胶体晶体的剪切模量G测量在几个恒定的颗粒密度n和不同的盐浓度c的熔融盐浓度cM使用扭转共振光谱。远离相边界的样品是多晶的，并且剪切模量作为c的函数大致保持恒定。在接近熔化转变时，围绕收缩的多晶芯形成增加量的壁基晶体材料，并且G几乎线性地下降。当跃迁完成时，G又保持不变。形态过渡可以在单个主曲线上缩放。对于多晶形态，弹性数据根据成对加性屏蔽库仑相互作用产生颗粒有效电荷Z（G）* 来评估。在去离子条件下，Z（0，G）* 与n无关，并且显著低于电荷重整化理论的预期。随着盐浓度的增加，Z（G）* 增加。在较大的n时，增加变得更加明显。通过外推，我们进一步得到了熔点有效弹性电荷Z（M，G）*。Z（M，G）* 随nM和cM的增加呈阶梯状增加，达到与电荷重整化理论一致的值。有趣的是，增加符合半定量与一个预期从通用的熔融线带电球，从而促进了一致的描述相行为和弹性在一个扩展的范围内的相图。
The shear modulus G of charged colloidal crystals was measured at several constant particle densities n and varying salt concentrations c up to the melting salt concentration cM using torsional resonance spectroscopy. Far from the phase boundary the samples are polycrystalline and the shear modulus stays roughly constant as a function of c. Upon approaching the melting transition an increasing amount of wall based crystal material is formed surrounding a shrinking polycrystalline core and G drops nearly linearly. When the transition is complete G again stays constant. The morphologic transitions may be scaled upon a single master curve. For the polycrystalline morphology, the elastic data are evaluated in terms of a pairwise additive screened Coulomb interaction yielding a particle effective charge Z(G)*. Under de-ionized conditions Z(0,G)* is independent of n and significantly lower than expected from charge renormalization theory. With increasing salt concentration Z(G)* increases. The increase becomes more pronounced at larger n. By extrapolation we further obtain the melting line effective elasticity charge Z(M,G)*. Z(M,G)* shows a steplike increase with increasing nM and cM to values consistent with charge renormalization theory. Interestingly, the increase coincides semi-quantitatively with the one expected from the universal melting line for charged spheres, thus facilitating a consistent description of phase behavior and elasticity over an extended range of the phase diagram.