| 查看: 2122 | 回复: 2 | |||
| 当前只显示满足指定条件的回帖，点击这里查看本话题的所有回帖 | |||
[求助]
请问什么是余辉长度(persistence length)？
|
|||
|
请问什么是余辉长度(persistence length)？ [ Last edited by mengsk on 2013-3-11 at 14:58 ] |
回复此楼» 猜你喜欢
酚醛树脂性能测试
已经有1人回复
-
香江学者计划2026年度申请启动！港科大李桂君教授课题组
已经有1人回复
-
无机非金属材料论文润色/翻译怎么收费?
已经有149人回复
-
求博导推荐
已经有1人回复
-
申博求助
已经有4人回复
-
材料方向博士，青岛
已经有2人回复
-
申博自荐
已经有4人回复
-
Energy and Environmental Science 期刊投稿-手稿格式问题，可单栏自由格式吗
已经有1人回复
-
深圳大学2026年招聘公告
已经有0人回复
-
中科南京智能技术研究院2026年招聘简章
已经有0人回复
-
匣钵烧结
已经有1人回复
|
Persistence length From Wikipedia The persistence length is a basic mechanical property quantifying the stiffness of a polymer. Informally, for pieces of the polymer that are shorter than the persistence length, the molecule behaves rather like a flexible elastic rod, while for pieces of the polymer that are much longer than the persistence length, the properties can only be described statistically, like a three-dimensional random walk. Formally, the persistence length, P, is defined as the length over which correlations in the direction of the tangent are lost. In a more chemical based manner it can also be defined as the average sum of the projections of all bonds j ≥ i on bond i in an indefinitely long chain.[1] Let us define the angle θ between a vector that is tangent to the polymer at position 0 (zero) and a tangent vector at a distance L away from position 0, along the contour of the chain. It can be shown that the expectation value of the cosine of the angle falls off exponentially with distance,[2] where P is the persistence length and the angled brackets denote the average over all starting positions. In polymer science jargon the persistence length is considered to be one half of the Kuhn length, the length of hypothetical segments that the chain can be considered as freely joined. The persistence length equals the average projection of the end-to-end vector on the tangent to the chain contour at a chain end in the limit of infinite chain length.[3] The persistence length can be also expressed using the bending stiffness , the Young's modulus E and knowing the section of the polymer chain.[4] In the case of a rigid and uniform rod I can be expressed as: where a is the radius. For example a piece of uncooked spaghetti has a persistence length on the order of m (taking in consideration a Young modulus of 0.1 GPa and a radius of 1 mm).[5] Double-helical DNA has a persistence length of about 500 Angstroms. |
3楼2013-03-13 15:15:09
huzhifeng09
专家顾问 (著名写手)
-
专家经验: +327 - 应助: 176 (高中生)
- 贵宾: 0.178
- 金币: 6710.3
- 红花: 31
- 帖子: 2084
- 在线: 159.7小时
- 虫号: 2313969
- 注册: 2013-03-03
- 性别: GG
- 专业: 高分子科学
- 管辖: 高分子
2楼2013-03-12 11:59:53