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      表面(mian)活性(xing)(xing)劑是(shi)指能夠使溶(rong)液(ye)表面(mian)張(zhang)力顯著降低的(de)(de)物(wu)質(zhi)。表面(mian)活性(xing)(xing)劑分(fen)子(zi)結(jie)構具有兩親性(xing)(xing)，一端由(you)非極(ji)性(xing)(xing)烴(jing)(jing)鏈(lian)（親油基(ji)）組成，烴(jing)(jing)鏈(lian)長度一般在8個碳(tan)原子(zi)以(yi)上，另一端由(you)一個以(yi)上極(ji)性(xing)(xing)基(ji)團(tuan)（親水(shui)基(ji)）組成。極(ji)性(xing)(xing)基(ji)團(tuan)可以(yi)是(shi)解(jie)離(li)的(de)(de)離(li)子(zi)，也可以(yi)是(shi)不(bu)解(jie)離(li)的(de)(de)親水(shui)基(ji)團(tuan)，如羧(suo)酸(suan)、磺酸(suan)、硫(liu)酸(suan)、磷酸(suan)、氨基(ji)或胺(an)(an)基(ji)及這些基(ji)團(tuan)的(de)(de)鹽，或者(zhe)羥基(ji)、酰胺(an)(an)基(ji)、醚(mi)鍵、羧(suo)酸(suan)酯基(ji)等。

       表(biao)面(mian)活(huo)性劑具有吸(xi)附性，在(zai)溶(rong)(rong)液(ye)中(zhong)呈現(xian)正吸(xi)附，當(dang)水(shui)中(zhong)表(biao)面(mian)活(huo)性劑的(de)濃度很低(di)時，表(biao)面(mian)活(huo)性劑分子(zi)在(zai)水(shui)-空氣(qi)界面(mian)產(chan)生(sheng)定(ding)向排列，親(qin)(qin)水(shui)基團朝向水(shui)而親(qin)(qin)油基團朝向空氣(qi)，從而在(zai)溶(rong)(rong)液(ye)表(biao)面(mian)聚集(ji)形成單(dan)分子(zi)層，溶(rong)(rong)液(ye)表(biao)面(mian)層表(biao)面(mian)活(huo)性劑濃度遠高于溶(rong)(rong)液(ye)中(zhong)的(de)濃度。正吸(xi)附改變了(le)溶(rong)(rong)液(ye)表(biao)面(mian)的(de)性質(zhi)，最外(wai)層呈碳氫(qing)鏈性質(zhi)，降低(di)了(le)溶(rong)(rong)液(ye)的(de)表(biao)面(mian)張力，從而產(chan)生(sheng)較好的(de)潤濕(shi)性、乳化(hua)性、起泡性等。

       表(biao)面(mian)(mian)活(huo)(huo)性(xing)(xing)(xing)(xing)劑(ji)具有吸(xi)附(fu)性(xing)(xing)(xing)(xing)，在(zai)(zai)溶液(ye)(ye)中(zhong)呈(cheng)現(xian)正吸(xi)附(fu)，當(dang)水(shui)中(zhong)表(biao)面(mian)(mian)活(huo)(huo)性(xing)(xing)(xing)(xing)劑(ji)的濃(nong)度(du)很低時，表(biao)面(mian)(mian)活(huo)(huo)性(xing)(xing)(xing)(xing)劑(ji)分子在(zai)(zai)水(shui)-空(kong)氣界面(mian)(mian)產生定向(xiang)排列(lie)，親水(shui)基團朝(chao)向(xiang)水(shui)而親油(you)基團朝(chao)向(xiang)空(kong)氣，從(cong)而在(zai)(zai)溶液(ye)(ye)表(biao)面(mian)(mian)聚(ju)集形成單(dan)分子層(ceng)，溶液(ye)(ye)表(biao)面(mian)(mian)層(ceng)表(biao)面(mian)(mian)活(huo)(huo)性(xing)(xing)(xing)(xing)劑(ji)濃(nong)度(du)遠高于溶液(ye)(ye)中(zhong)的濃(nong)度(du)。正吸(xi)附(fu)改變了(le)溶液(ye)(ye)表(biao)面(mian)(mian)的性(xing)(xing)(xing)(xing)質(zhi)，最外層(ceng)呈(cheng)碳氫(qing)鏈性(xing)(xing)(xing)(xing)質(zhi)，降(jiang)低了(le)溶液(ye)(ye)的表(biao)面(mian)(mian)張(zhang)力，從(cong)而產生較好的潤濕性(xing)(xing)(xing)(xing)、乳化性(xing)(xing)(xing)(xing)、起泡(pao)性(xing)(xing)(xing)(xing)等。

       表(biao)面(mian)(mian)(mian)活性(xing)(xing)溶(rong)液與固(gu)體(ti)接觸時，也(ye)能(neng)在其表(biao)面(mian)(mian)(mian)發(fa)生(sheng)吸(xi)(xi)(xi)附，使固(gu)體(ti)表(biao)面(mian)(mian)(mian)性(xing)(xing)質改(gai)變。非極性(xing)(xing)固(gu)體(ti)表(biao)面(mian)(mian)(mian)呈單層(ceng)吸(xi)(xi)(xi)附，親(qin)(qin)油基(ji)吸(xi)(xi)(xi)附在固(gu)體(ti)表(biao)面(mian)(mian)(mian)而(er)親(qin)(qin)水(shui)基(ji)朝向(xiang)空氣(qi)，并(bing)且吸(xi)(xi)(xi)附量并(bing)不隨表(biao)面(mian)(mian)(mian)活性(xing)(xing)劑濃度的(de)(de)(de)增加而(er)增加，甚至有減(jian)少的(de)(de)(de)趨(qu)勢。極性(xing)(xing)固(gu)體(ti)表(biao)面(mian)(mian)(mian)既能(neng)單層(ceng)吸(xi)(xi)(xi)附也(ye)能(neng)發(fa)生(sheng)多層(ceng)吸(xi)(xi)(xi)附。在低濃度下(xia)，表(biao)面(mian)(mian)(mian)活性(xing)(xing)劑分子在極性(xing)(xing)固(gu)體(ti)表(biao)面(mian)(mian)(mian)的(de)(de)(de)吸(xi)(xi)(xi)附曲線為S形，形成(cheng)單分子層(ceng)。當濃度達到臨界膠(jiao)束濃度時，吸(xi)(xi)(xi)附達到飽和而(er)呈現雙層(ceng)吸(xi)(xi)(xi)附，表(biao)面(mian)(mian)(mian)活性(xing)(xing)劑分子的(de)(de)(de)排列方向(xiang)與第一層(ceng)相反，親(qin)(qin)水(shui)基(ji)團(tuan)朝向(xiang)空氣(qi)，吸(xi)(xi)(xi)附量隨著(zhu)溶(rong)液溫度的(de)(de)(de)升高而(er)減(jian)少。