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聚乙烯在不良溶剂中高温结晶时 ,往往在 { 2 0 0 }面形成弧形边 .因为不良溶剂的影响 ,此时形成的临界核长度较短 .这种薄的片晶在高温条件下是热力学不稳定的 ,在缓慢的单晶生长过程中不可避免地伴随着退火的过程 .在片晶生长的前沿仍然保持着临界核厚度的同时 ,它的中心部分已经由于退火作用而增厚 .这就使得所得单晶从中心到边缘具有一定的厚度梯度 (即中间厚 ,边缘薄 ) .另一方面 ,晶胞参数与片晶的厚度有关 :在较厚的片晶中晶胞较小 ,而在较薄的片晶中晶胞较大 .因此 ,在前述具有厚度梯度的片晶中 ,从中心到边缘晶胞尺寸逐渐增大 .这种变化在晶格中产生了一种应力 ,必然引起晶格的应变 .如果主要生长面{ 110 }的边变成同一套具有巨大半径的同心圆的圆弧 ,晶格的排列就可适应上述晶胞尺寸的变化 .由于同心圆的半径很大 ,而单晶中 { 110 }面的边只是圆弧的很小一部分 ,故仍然接近直线 .与此同时 ,生长较慢的 { 2 0 0 }面的边却随之变为椭圆的一部分 ,具有明显的曲率 .
When polyethylene is crystallized in a poor solvent at a high temperature, it tends to form arcuate edges on the {2 0 0} surface because of the short critical nuclei formed at this time due to poor solvents. The thermodynamically unstable, unavoidably accompanied annealing process during slow single crystal growth, has its central part thickened by the annealing, while still maintaining the critical thickness at the front of the growth of the slab. The resulting single crystal has a certain thickness gradient from the center to the edge (ie middle thickness, thin edge) On the other hand, the unit cell parameters are related to the thickness of the platelet: the unit cell is smaller in the thicker platelet In the thinner platelets, the unit cell is larger, so in the platelet with the thickness gradient described above, the size of the unit cell from the center to the edge is gradually increased, and this change causes a stress in the crystal lattice which inevitably causes Lattice Strain If the edges of the principal growth plane {110} become the same set of concentric circular arcs with large radii, the arrangement of the lattice can be adapted to the above-mentioned changes in the size of the unit cell. Due to the large radius of the concentric circle, The single crystal in the {110} plane The edge is only a small part of the arc, so it is still close to a straight line, while the edge of the slower growing {2 0 0} surface becomes a fraction of an ellipse with a significant curvature.