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zhaobingscu金蟲(chóng) (正式寫(xiě)手)
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[交流]
聚合物溶解存在飽和點(diǎn)嗎?
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近來(lái)在做一些聚合物的溶解實(shí)驗(yàn),突然想到一個(gè)問(wèn)題,聚合物是否像小分子一樣存在溶解度的概念?也就是存在一個(gè)飽和點(diǎn)。我記得以前學(xué)習(xí)過(guò)一篇英文課文,把他找出來(lái)了,如下 Another striking difference with respect to the behavior of a polymer and that of a low molecular weight compound concerns the dissolution process. Let us take, for example, sodium chloride and add it slowly to s fixed quantity of water. The salt, which represents a low molecular weight compound, dissolves in water up to s point (called saturation point) but, thereafter, any further quantity added does not go into solution but settles at the bottom and just remains there as solid. The viscosity of the saturated salt solution is not very much different from that of water. But if we take a polymer instead, say, polyvinyl alcohol, and add it to a fixed quantity of water, the polymer does not go into solution immediately. The globules of polyvinyl alcohol first absorb water, swell and get distorted in shape and after a long time go into solution. Also, we can add a very large quantity of the polymer to the same quantity of water without the saturation point ever being reached. As more and more quantity of polymer is added to water, the time taken for the dissolution of the polymer obviously increases and the mix ultimately assumes a soft, dough-like consistency. Another peculiarity is that, in water, polyvinyl alcohol never retains its original powdery nature as the excess sodium chloride does in a saturated salt solution. In conclusion, we can say that (1) the long time taken by polyvinyl alcohol for dissolution, (2) the absence of a saturation point, and (3) the increase in the viscosity are all characteristics of a typical polymer being dissolved in a solvent and these characteristics are attributed mainly to the large molecular size of the polymer. The behavior of a low molecular weight compound and that of a polymer on dissolution are illustrated in Fig.1.2. 發(fā)現(xiàn)另一種不同的聚合物行為和低分子量化合物行為是關(guān)于溶解過(guò)程。例如,讓我們研究一下,將氯化鈉慢慢地添加到固定量的水中。鹽,代表一種低分子量化合物,在水中達(dá)到點(diǎn)(叫飽和點(diǎn))溶解,但,此后,進(jìn)一步添加鹽不進(jìn)入溶液中卻沉到底部而保持原有的固體狀態(tài)。飽和鹽溶液的粘度與水的粘度不是十分不同,但是,如果我們用聚合物替代,譬如說(shuō),將聚乙烯醇添加到固定量的水中,聚合物不是馬上進(jìn)入到溶液中。聚乙烯醇顆粒首先吸水溶脹,發(fā)生形變,經(jīng)過(guò)很長(zhǎng)的時(shí)間以后進(jìn)入到溶液中。同樣地,我們可以將大量的聚合物加入到同樣量的水中,不存在飽和點(diǎn)。將越來(lái)越多的聚合物加入水中,認(rèn)為聚合物溶解的時(shí)間明顯地增加,最終呈現(xiàn)柔軟像面團(tuán)一樣粘稠的混合物。另一個(gè)特點(diǎn)是,在水中聚乙烯醇不會(huì)像過(guò)量的氯化鈉在飽和鹽溶液中那樣能保持其初始的粉末狀態(tài)?傊覀兛梢灾v(1)聚乙烯醇的溶解需要很長(zhǎng)時(shí)間,(2)不存在飽和點(diǎn),(3)粘度的增加是典型聚合物溶于溶液中的特性,這些特性主要?dú)w因于聚合物大分子的尺寸。 上文說(shuō)聚乙烯醇在水中的溶解沒(méi)有飽和點(diǎn),那我想問(wèn)其他聚合物在他的良溶劑的溶解也沒(méi)有飽和點(diǎn)嗎? |
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金蟲(chóng) (知名作家)
木蟲(chóng) (小有名氣)
木蟲(chóng)之王 (文學(xué)泰斗)
金蟲(chóng) (職業(yè)作家)
木蟲(chóng) (職業(yè)作家)
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我也想過(guò)聚合物溶解是否存在溶解度,也就是您所說(shuō)的飽和點(diǎn) 也許有吧 我說(shuō)不清 聚合物的溶解行為和小分子不一樣,聚合物相對(duì)于水分子太大了 向非晶水溶性聚合物中,看起來(lái)聚合物逐漸溶脹,當(dāng)水量剛到一點(diǎn)時(shí),就溶解了。感覺(jué)像有飽和點(diǎn) |
木蟲(chóng) (職業(yè)作家)
金蟲(chóng) (小有名氣)
銅蟲(chóng) (小有名氣)
| 聚合物溶解是分不同種類的,有結(jié)晶聚合物,和非晶態(tài)的,其溶解的時(shí)候是分子鏈通過(guò)溶劑化作用調(diào)整構(gòu)象以分子形式分散在溶劑中,有一個(gè)容度參數(shù),而且其溶解時(shí)粘度增大, 所謂的飽和,就是你所標(biāo)定的粘度達(dá)到一定得值,高分子溶解不是小分子溶解存在飽和蒸汽壓,只是鏈的分散?梢詤⒖己温母叻肿游锢 |
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