本文是針對聚電解質（polyelectrolyte）在水溶液中的反離子凝聚現象進行研究。由之前文獻中可知聚電解質種類有非常多種，我們整理出陰離子型聚電解依官能基可分為三類：磷酸根、羧酸根和磺酸根；陽離子型為銨根和硫根，由內我們選用結構式最簡單的Poly(acrylic acid, sodium salt, NaPAA）、Poly(sodium styrene sulfonate, NaPSS)和poly(diallyldimethylammonium chloride, PDDC)來探討聚電解質的一些物理特性。 在聚電解質溶液中，聚電解質會解離出相反離子，因本身帶有強大的電荷，反離子受靜電作用力影響，則會被吸附到聚電解質附近，因而使本身應帶有的有效電荷減少，這個現象就稱為反離子凝聚現象。此現象最常應用在工業廢水處理和醫學方面的研究。 早在40年代在研究聚電解質的時候，就已經有許多的學者用NaPSS作為研究聚電解質特性的標準物，其實驗報告方向均集中在黏度、滲透壓及導電度等。我們實驗選用陰離子型（NaPAA和NaPSS）和陽離子型（PDDC）的聚電解質來探討聚電解質在dilute和semi-dilute溶液中salt-free或添加鹽類所造成的凝聚現象研究，並探討聚電解質在salt-free溶液中，分子量、濃度和介電係數對聚電解質的影響，做一系列相關實驗的比較。 聚電解質NaPSS和NaPAA可溶於水，並在溶液中形成單一分子鏈(single chain)，或是由數各分子經由counterion產生的離子聚集(ionic cluster)；但是相對的，鹽類對聚電解質而言為一疏水性溶質，並不易在鹽類溶液中解離成離子態，所以NaPSS和NaPAA在不同比例混合的多價鹽類/水溶液中，可能會有不同的分子形態。我們的實驗目的希望能藉由離子濃度儀所測得之電位，代入 Nerst Equention求得的離子濃度，來觀察聚電解質水溶液、NaPSS/鹽類/水和NaPAA/鹽類/水反離子凝聚現象的程度，並可利用自由反離子濃度和所有反離子濃度的比值來判定此現象的程度，此即稱為解離度（degree of ionization）。 在實驗結果中我們發現，聚電解質在salt-free溶液中，藉由改變聚電解質的分子量，解離度會隨著分子量增加而下降，我們也利用滲透壓法證實這個實驗結果的準確度。改變聚電解質濃度，則溶液濃度在dilute情況下，當系統達熱力學平衡時，解離度隨著濃度上升而下降；下降至某一程度後，則因亂度下降量跟靜電作用力上升量已不太明顯，所以解離度為一定值。改變溶液的介電係數，則隨著介電係數增加，靜電作用力越弱，反離子凝聚現象越不明顯，其解離度會上升。 在聚電解質溶液中加入一價鹽類，結果發現鹽類會使聚電解質的反離子凝聚現象越趨明顯；若同為一價鹽類競爭，其競爭強度為H+>Li+>Na+>K+>Rb+>Cs+，由此知鋰離子較易被吸附到聚電解質附近，而使聚電解質解離度增加；當加入多價鹽類時，價數越高，則靜電吸引力越強，所以取代凝聚反離子的能力也越強。但是，加到某一濃度時，發現NaPAA聚電解質有沈澱現象而NaPSS沒有，以靜電作用力來說，兩者現象應該是一樣的，所以可能跟他們的化學結構有關，由文獻知道，NaPAA其官能基跟螯合物中最強的配基乙二胺四乙酸根 (Ethylenediaminetetraacetate, EDTA)結構類似，當EDTA遇到任何多價的離子，會產生螯合現象，易產生沈澱現象；因此我們在NaPAA溶液中添加比羧酸根還強的配基NH3，結果發現多價金屬離子會和NH3形成錯離子而使沈澱消失，表示二價金屬是與NAPAA形成錯合物而沈澱；接下來我們也由FTIR實驗證明NaPAA與多價鹽類會產生沈澱，是因為添加過程中也產生了螯合鍵結反應。 A polyelectrolyte dissolves in water, leaving ionized charged groups on the polymer backbone and counterions in the solution. Counterions are not distributed uniformly in the solution but prefer to stay in the neighborhood of the oppositely charged polymer. The extent of counterions residing near the polyelectrolyte mediates how polymers interact among themselves and thereby influence the physical properties of a polyelectrolyte solution. Counterion condensation around linear polyelectrolyte chains (sodium polyacrylate & sodium polystyrene sulfonate) is investigated in terms of the degree of ionization α, which is proportional to the effective charge. On the basis of counterion chemical potential, the effective charge of polyelectrolytes is directly determined by the ion-selective electrode and the degree of ionization is simply defined as the ratio of measured to intrinsic (complete ionization) counterion concentration, α ≣ co/ci. In the dilute regime, the degree of ionization decreases with increasing the molecular weight (Mw) and the polymer concentration (cp). This result is consistent with the prediction by Monte Carlo simulation and can be qualitatively explained by a simple model of two-phase approximation. In the semi-dilute regime, the degree of ionization becomes insensitive to cp. The counterion entropy loss seems to tie with the decrease of Coulombic attraction due to polyelectrolyte - polyelectrolyte interactions. As the molecular weight is increased at constant monomer concentration, α declines first but becomes insensitive to Mw. This consequence reveals that as the polyelectrolyte is long enough, however, the entanglement effects are indistinguishable. The degree of ionization based on ion-selective electrode agrees with that obtained from osmometry but deviates from that by conductometry. This result indicates that the primary contribution to the osmotic pressure of a polyelectrolyte solution comes from the free counterion concentration.
