Uncle chimpanzee

There is a heated debate among the Chinese science blogosphere science.net/blogs about scientific instruments. Research of physcial sciences in China has long been suffereing from expensive imported equipments. As I estimate over 90% instruments used in China are imported from abroad. It seems quite reasonable if we look at specific type of instruments like DSC or TEM. The best brands of thermal analyzer may be TA or Netzsch, for example, and for rheometers there are Anton Paar, Malven, and also TA. JEOL, Phillips and Hitachi lead the market of electron microscopes. None of these companies are China based. Import is inevitable for not only China but countries other than those the above companies belong to. However, for years the national education investment in China have been lower than 3% of the GDP, and a large number of young Chinese scientists do feel great finacial pressure to start their own laboratory. What’s worse, laboratories here always charge a high price for sharing their own instruments. All of these stimulate discussion of the absence of domestic products available in the market.

The obstacle for China’s own scientific instrument companies is intuitively the low status of manufacturing industry, especially high precision, high sensitive parts production. There are indeed a number of allegedly domestic DSC or even TEM but surely these are assembly of imported parts. You will immediately understand what I mean if you think about the made-in-China products in your country: there is no high quality production in China now. Manufacturers are reluctant to invest in technology innovation because simple copying and assembling things makes enough money.

Why? Because there is no protection of innovation here! Discourage of innovation has also created bad atmosphere for youth. Graduate students from China tend to use any equipment passively, according or even not according to the user manuals. They only press the buttons on the panel or use the beginner’s wizard of the softwares. They may know little or none about the principle, structure, electric circuits inside the instrument, and have no disire and base to modify the equipment for better experimental aim or result. They lack the ability of DIY. There is also no workshops in most labs in China. Even you want to DIY something you find huge difficulty in getting all the tools and materials from the lab or market.

My boss told me that when he was a PhD student in Japan there used to be the “uncle Chimpanzee” (チンパンジーのおじさん, chinpanjī no ojisan, using Google Translate) who came to their lab from time to time. Any requirement of modified parts or DIY project could be discussed with him, who know a little of nearly everything. Personalized stuffs could thus realized most of the time. Now as I know every labs in the US have a properly designed workshop. Tools and materials are available from all kind of catelogues. Parts are all standardized. These exist because people need them. There will be none if they are needless, as is the case in China.

I think our people should use less Microsoft software and turn to free, open-source product to avoid the necessity of piracy and harm to IP rights, and in the long run culture the culture of innovation. In this way, Google should not be ban by China. It is more a friend than Microsoft because many of Google’s products are free and cutting edge. I wish one day all Chinese computers suddenly shift to Chrome OS and a large money will released from paying for the software licsense and used instead in domestic intellectural properties.

凝胶化过程的非线性粘弹性

ResearchBlogging.org

熟悉溶液-凝胶转变(sol-gel transition)的朋友应该知道渝渗(percolation)理论。流变学上,H. Winter从高分子凝胶的实验提出的临界凝胶指数也“众”所周知:

至于指数n与渝渗理论的分形指数df之间的关系则要考虑高分子链的排除体积、分子量分布等问题,用得比较多的是M. Muthukumar的关系式:

我们课题组之前在也做了一些这方面的工作。

渝渗理论把凝胶化看成一种相变,还基于这样一个基本现象:在凝胶化初期,样品中发生局部交联而形成团簇,溶液的零切粘度不断增大,在临界点之前发散,说明形成了无限网络,失去流动性;临界点后体系显示非零的平衡模量,并随着网络的继续完善而不断增大,形成凝胶。我导师曾经猜想,在临界点附近,不管是之前还是之后,体系的非牛顿性会非常大,显示出较明显的非线性粘弹性,而在初期的溶液状态,体系是牛顿流体;在后期的完善凝胶状态,体系是虎克弹性体,两种情况的非线粘弹性粘弹性都不明显。也就是说不光可以用H. Winter的线性粘弹性方法找到临界凝胶点,还可以通过非线性的流变实验方法来定义临界凝胶点,具体就是当时刚热门起来的所谓LAOS。可是,我在聚丙烯酸/铁(III)凝胶体系上花了一年时间,都没做出这样的结果来。我采用的主要是M. Wilhelm提的Fourier变换流变学的方法,我的结果是在Winter凝胶点前后,I3/1单调增加,没有什么最大值。而且数据很烂,很难做到适合发表的程度。

我的结果

我做的结果

其实,实验时不得不采用的大幅形变,把样品形成的网络结构都破坏了,出来的结果都不是那个凝胶了,而是网络破坏之后的流体,所以用LAOS无法证实我导师的猜想。想来,LAOS也许只适合去研究“破坏什么东西”的过程或体系(非平衡态),不适合去研究“形成了什么东西”的过程或体系(平衡态),因此后来我和放弃了这个实验,转而做别的去了。现在非线性流变学方面的热点转到屈服流体上,可能也是因为上述原因。

这两天看到Rheol. Acta上的一篇文章:

Andrade, R., Azevedo, A., Musampa, R., & Maia, J. (2010). Thermo-rheological behavior of model protein–polysaccharide mixtures Rheologica Acta DOI: 10.1007/s00397-010-0431-3

做的是多糖/蛋白体系热致凝胶化,倒是使用了一下LAOS,做了凝胶化过程的I3/1 vs γ0图,结果是凝胶化点前后,曲线按形状可明显分为两堆(见下图),凝胶化之前的体系非线性粘弹性比凝胶化之后大得多。我相信这些结果也是反映的也是网络已被破坏后结果,对凝胶网络的形成过程没有什么参考作用。

文章的结果

文章的结果

顺便说明一下,上图是我使用Engauge Digitizer软件从文章的PDF文件移植出来的数据,用Origin重新作的图。Engauge Digitizer的功能是从静态的图片文件格式的坐标曲线中抓取数据,重新生成数据文件的软件。做流变学研究,经常要理论和实验两边跑。经常要拿他人发表的数据按照重新代入新的方程来运算。用这个软件,就可以从PDF文章截下坐标图,转化成数据文章,进行进一步的运算了。这是开源软件,免费的,在此推荐一下。

也就是说LAOS这个东西如果要做,目前暂时还具体体系具体分析。凝胶化方面,没有什么理论支持。按渝渗理论猜想出来的东西是不存在的,或者如果像Muthukumar那样,严格地推导一下大幅形变场下的行为,会有什么有意义的结果?

Rheol. Acta这篇文章还提到了Hyun等人曾经报道的I3/1 vs γ0的初始斜率问题(log-log图下),线形高分子体系斜率为2,支化体系斜率小于2。Rheol. Acta这篇文章的初始斜率为1.4,按Hyun的观点,那就是一个非常支化的体系。这又让我动了心思:既然LAOS做的是网络破坏后的体系,那么,没形成网络前,是“破坏”不出来“支化结构的”;只有网络形成后,“破坏”的结果才会是一种支化结构的混合物。如果用I3/1 vs γ0的初始斜率来表征,那么凝胶点附件,斜率应该从突降,在该处就能定义一个非线性的临界点了。结果是不是这样呢?我用Rheol. Acta这篇文章的数据试了一下,发现它做的斜率也没有什么规律,勉强说也是“突增”,而且并不发生在Winter凝胶点附近。又没戏!

没戏!

没戏!

所以再次说明yield stress fluid为什么火!人家起码有个SGR理论比较好用的。

ScienceDirect的Top 25网页

偶然发现ScienceDirect有个网页,可以显示其旗下期刊的Top 25热文(估计是算下载次数)。

流变学方面ScienceDirect有个Journal of Non-Newtonian Fluid Mechanics,它上一季度的Top 25见此。近来,屈服应力流体(yield stress fluid)以及与其相关的悬浮体系流变学突然热门起来,也可以体现在与2008年情况的比较上,尤其是Barnes的那篇思考屈服应力本质的老文章,突然又重新热起来,排到第二位。我之前曾经评论过那篇文章