半稀釋聚乙烯醇-硼酸鈉水溶液之動態光散射研究

Dynamic Light Scattering of poly(vinyl alcohol)-borax Semidilute Solutions

巫思丘(S.C. Wu)

指導教授 ： 余子隆

元智大學/工程學院/化學工程與材料科學學系/碩士(1997年)

摘要

本研究是利用動態光散射儀,在不同散射角度,
研究在水溶液中PVA-硼酸鹽錯離子鬆弛時間隨硼酸鈉濃度變化之情形,
藉以瞭解其分子鏈的運動情形。
光散射實驗溫度為25℃,散射角度Θ=30o,45o,60o,90o及120o。聚乙烯醇濃度固定為40g/L,
硼酸鈉溶液濃度為0,0.006,0.01,0.02,….0.20M。PVA的重疊濃度約為15g/L,
故本實驗濃度屬於半稀釋溶液範圍,聚乙烯醇與硼酸離子可能同時產生分子內與分子間交聯反應。
隨著硼酸鈉濃度的增加,系統內自由硼酸負離子與自由鈉離子有著明顯的改變。聚合體上負離子的排斥效應,
自由鈉正離子對聚乙烯醇-硼酸負離子的遮蔽效應,聚乙烯醇的排斥體積, 及分子內與分子間交聯反應,
使得聚乙烯醇-硼酸鈉錯離子分子鏈隨著硼酸鈉濃度的增加有膨脹、收縮的現象稱之re-entrant為現象。
實驗結果發現有四個鬆弛模式區(solvent mode tsol, fast mode tf, middle mode tm, 及 slow mode ts)。
短時間鬆弛模式(tf)是由兩交聯點間分子鏈運動產生的鬆弛行為所形成,
而長時間鬆弛模式(ts)則是由聚乙烯醇-硼酸鈉錯離子聚合物形成的分子團(cluster)運動所產生。
tm及tf鬆弛態的鬆弛速率與sin2(Θ/2)呈線性關係,所以屬於diffusive mode。
DLS數據顯示在t < 1 ms附近處有一個短時間鬆弛模式(tsol),此為溶劑運動的鬆弛波峰。
在硼酸鈉濃度高於0.14 M以上,可能是溶液系統形成凝膠,動態光散射無
法偵測到ts鬆弛峰。

關鍵字

聚乙烯醇 ； 硼酸鈉 ； 動態光散射 ； 半稀釋溶液

並列摘要

Dynamic light scattering (DLS) was used to study the solution property of poly(vinyl alcohol)-borax
(PVA-borax) semidilute solutions with a PVA concentration of 40g/L and borax concentrations varied from 0.0 M to 0.2 M.
The DLS experiments were carried out at 25℃ with various scattering angles
(i.e Θ=30o,45o,60o,90o and 120o). Four relaxation modes (tsol,tf,tm, and ts) were observed from the DLS correlation functions .
The mode (tsol ) with the relaxation time tsol shorter than 1 ms was attributed the solvent diffusive mode ;
the mode (tf ) with a relaxation time around 10-4 sec was attributed to the relaxation of molecular chain between two entanglements ;
the mode (tm) with a relaxation time around 10-1 sec was attributed to the relaxation of small PVA cluster bound through H-bond;
and the mode which had the longest relaxation time (ts ) with ts longer than 1 sec was attributed to the motion of large PVA
cluster bound through H-bond and borate ion. The ts , tm and tf are all angular dependent indicating they are diffusive modes.
As the borax concentration was higher than 0.14 M, the slow mode (ts) was not observed on the DLS
correlation functions suggesting that PVA-borax system may form a gel as the borax concentration was higher than 0.14 M.

並列關鍵字

Poly(vinyl alcohol) ； borax ； dynamic light scattering ； semidilute solution

參考文獻

r Brown,W.,"Slow mode diffusion in semidilute solutions examined by

dynamic light scattering "Macromolecules,17,66 (1984)

solution-dynamic light scattering and gradient diffusion "Polymer, 26,1647 (1985)

r Brown,W.,"Dynamics of semidilute solutions using photon-correlation

relaxation times from quasi-elastic light scattering