徐廣春(chun)，顧(gu)中言，徐德進，許小龍

目的研究水(shui)稻(dao)葉(xie)片(pian)(pian)的表(biao)面(mian)(mian)(mian)特性(xing)和有(you)機硅(gui)助(zhu)劑Silwet-408溶液(ye)(ye)(ye)的單(dan)(dan)個(ge)霧(wu)滴在30°、45°和60°3個(ge)傾(qing)(qing)角水(shui)稻(dao)葉(xie)片(pian)(pian)正、反面(mian)(mian)(mian)的行(xing)為(wei)，以期(qi)為(wei)農藥(yao)霧(wu)滴對靶葉(xie)面(mian)(mian)(mian)滯留控制機制提供依(yi)據。方法利用掃描(miao)電(dian)鏡觀察水(shui)稻(dao)葉(xie)片(pian)(pian)的表(biao)面(mian)(mian)(mian)特性(xing)，并通(tong)過Zisman圖法測定(ding)(ding)稻(dao)葉(xie)的臨界(jie)表(biao)面(mian)(mian)(mian)張力。同時測定(ding)(ding)0、3.91、7.81、15.63、31.25、62.50、125.00和250.00 mg·L-18個(ge)濃(nong)(nong)度的Silwet-408溶液(ye)(ye)(ye)的表(biao)面(mian)(mian)(mian)張力后(hou)，利用表(biao)面(mian)(mian)(mian)張力法測定(ding)(ding)出(chu)Silwet-408的臨界(jie)膠束濃(nong)(nong)度，并借助(zhu)于接(jie)觸(chu)(chu)角測量儀測定(ding)(ding)8個(ge)溶液(ye)(ye)(ye)的單(dan)(dan)個(ge)霧(wu)滴在3個(ge)傾(qing)(qing)角水(shui)稻(dao)葉(xie)片(pian)(pian)上的接(jie)觸(chu)(chu)角。

結(jie)果(guo)電(dian)鏡觀察發現水稻(dao)葉(xie)片(pian)正、反面(mian)存在3種類型的(de)絨毛(mao)，同時表(biao)面(mian)布(bu)滿了乳頭狀的(de)突起，其密度分(fen)別為(wei)(wei)(wei)（12.4±0.7）×103和（7.6±0.8）×103個(ge)/mm2且(qie)差(cha)異顯著；氣孔長(chang)度和氣孔密度間均(jun)無顯著差(cha)異。Silwet-408的(de)臨界(jie)膠(jiao)束(shu)濃(nong)度為(wei)(wei)(wei)78.5 mg·L-1，與之相對應的(de)溶(rong)(rong)(rong)液(ye)(ye)的(de)表(biao)面(mian)張(zhang)力為(wei)(wei)(wei)20.77 mN·m-1。水稻(dao)葉(xie)片(pian)正、反面(mian)的(de)臨界(jie)表(biao)面(mian)張(zhang)力估值分(fen)別為(wei)(wei)(wei)29.90和31.22 mN·m-1。在所(suo)測定的(de)溶(rong)(rong)(rong)液(ye)(ye)中，濃(nong)度為(wei)(wei)(wei)0、3.91、7.81 mg·L-1溶(rong)(rong)(rong)液(ye)(ye)的(de)表(biao)面(mian)張(zhang)力大于稻(dao)葉(xie)的(de)臨界(jie)表(biao)面(mian)張(zhang)力且(qie)Silwet-408濃(nong)度小于臨界(jie)膠(jiao)束(shu)濃(nong)度，這3個(ge)濃(nong)度溶(rong)(rong)(rong)液(ye)(ye)的(de)霧(wu)滴將直接從不同傾角水稻(dao)葉(xie)片(pian)上滾落。

濃(nong)度為15.63、31.25、62.50 mg·L-1溶液(ye)(ye)的(de)(de)(de)(de)(de)(de)表(biao)面(mian)(mian)張力小(xiao)于稻葉(xie)的(de)(de)(de)(de)(de)(de)臨(lin)(lin)界表(biao)面(mian)(mian)張力且Silwet-408濃(nong)度小(xiao)于臨(lin)(lin)界膠束濃(nong)度，15.63和(he)(he)(he)31.25 mg·L-1溶液(ye)(ye)的(de)(de)(de)(de)(de)(de)霧滴在(zai)(zai)(zai)傾(qing)角(jiao)較(jiao)(jiao)低時(shi)(shi)（30°）能(neng)(neng)黏(nian)附葉(xie)片(pian)上(shang)，較(jiao)(jiao)高時(shi)(shi)（60°）滾落；62.50 mg·L-1溶液(ye)(ye)的(de)(de)(de)(de)(de)(de)霧滴能(neng)(neng)黏(nian)附在(zai)(zai)(zai)稻葉(xie)上(shang)，不同傾(qing)角(jiao)間(jian)的(de)(de)(de)(de)(de)(de)接觸角(jiao)變(bian)(bian)化率和(he)(he)(he)潤(run)濕(shi)滯后存在(zai)(zai)(zai)差異；125.00和(he)(he)(he)250.00 mg·L-1溶液(ye)(ye)的(de)(de)(de)(de)(de)(de)表(biao)面(mian)(mian)張力小(xiao)于稻葉(xie)的(de)(de)(de)(de)(de)(de)臨(lin)(lin)界表(biao)面(mian)(mian)張力且Silwet-408濃(nong)度大于臨(lin)(lin)界膠束濃(nong)度，這2個溶液(ye)(ye)的(de)(de)(de)(de)(de)(de)霧滴均能(neng)(neng)黏(nian)附在(zai)(zai)(zai)不同傾(qing)角(jiao)的(de)(de)(de)(de)(de)(de)水稻葉(xie)片(pian)上(shang)，40 s后的(de)(de)(de)(de)(de)(de)接觸角(jiao)變(bian)(bian)化率和(he)(he)(he)潤(run)濕(shi)滯后無顯著差異。不同傾(qing)角(jiao)稻葉(xie)上(shang)霧滴的(de)(de)(de)(de)(de)(de)前(qian)進角(jiao)（θa）和(he)(he)(he)后退角(jiao)（θr）的(de)(de)(de)(de)(de)(de)分(fen)析結(jie)果表(biao)明θa總(zong)是(shi)大于θr，在(zai)(zai)(zai)40 s的(de)(de)(de)(de)(de)(de)測(ce)定時(shi)(shi)間(jian)內，隨時(shi)(shi)間(jian)延遲θa和(he)(he)(he)θr總(zong)是(shi)逐漸(jian)減(jian)少。

結論稻(dao)(dao)(dao)葉(xie)(xie)(xie)的(de)(de)強(qiang)疏水性主要歸因于其表(biao)(biao)面布滿了(le)包被著蠟(la)質的(de)(de)乳頭狀突起(qi)，同時這還可能與(yu)其葉(xie)(xie)(xie)表(biao)(biao)面的(de)(de)毛長(chang)和氣孔密(mi)度密(mi)切(qie)相關(guan)。水稻(dao)(dao)(dao)葉(xie)(xie)(xie)面為低(di)能葉(xie)(xie)(xie)面。只有Silwet-408溶液(ye)的(de)(de)表(biao)(biao)面張(zhang)力小于稻(dao)(dao)(dao)葉(xie)(xie)(xie)的(de)(de)臨(lin)界表(biao)(biao)面張(zhang)力且溶液(ye)中的(de)(de)Silwet-408濃度達(da)到臨(lin)界膠束(shu)濃度才能使霧(wu)滴(di)很(hen)好的(de)(de)黏附(fu)在不(bu)同傾角(jiao)的(de)(de)稻(dao)(dao)(dao)葉(xie)(xie)(xie)上并潤(run)濕展布；過低(di)濃度的(de)(de)溶液(ye)的(de)(de)霧(wu)滴(di)由于較大的(de)(de)表(biao)(biao)面張(zhang)力易從不(bu)同傾角(jiao)的(de)(de)稻(dao)(dao)(dao)葉(xie)(xie)(xie)上滾落(luo)。Silwet-408溶液(ye)的(de)(de)霧(wu)滴(di)在不(bu)同傾角(jiao)葉(xie)(xie)(xie)片上的(de)(de)θa大于θr形成(cheng)的(de)(de)潤(run)濕滯后說明了(le)稻(dao)(dao)(dao)葉(xie)(xie)(xie)表(biao)(biao)面的(de)(de)粗糙，而這種粗糙與(yu)稻(dao)(dao)(dao)葉(xie)(xie)(xie)表(biao)(biao)面存在的(de)(de)高密(mi)度乳突密(mi)切(qie)相關(guan)。

Characteristics of Rice Leaf Surface and Droplets Deposition Behavior on Rice Leaf Surface with Different Inclination Angles

XU Guang-chun，GU Zhong-yan，XU De-jin，XU Xiao-long

Scientia Agricultura Sinica，2014，47(21):4141-4154

Objective]In order to provide a basis of mechanisms controlling retention of pesticide droplets on target leaf，characterization of rice leaf surface and behavior analysis of single droplets of trisiloxane surfactant(Silwet-408)solutions on rice leaf surface with different inclination angles were studied.[Method]Scanning electron microscope(SEM)was used for observation of rice leaf surface characteristics and the critical surface tension(CST)of rice leaf was determined by Zisman method.Surface tension of Silwet-408 solutions at concentrations of 0，3.91，7.81，15.63，31.25，62.50，125.00 and 250.00 mg·L-1 was measured and the critical micelle concentration(CMC)of Silwet-408 was also measured according to the change of surface tension of Silwet-408 solutions.Then the contact angle of a single droplet on the rice leaf surface with 3 inclination angles was determined by contact angle meter.[Result]SEM images showed that 3 types of hairs and densely covered papillae were observed on both the adaxial and abaxial sides of rice leaf.Densities of papillae，with significant difference between the adaxial and abaxial rice leaf surface，were((12.4±0.7)×103)and((7.6±0.8)×103)/mm2，respectively.In contrast，no significant differences in stomatal length or stomatal density were found.The CMC of Silwet-408 was 78.5 mg·L-1 and surface tension value of correspondingsolution at CMC was 20.77 mN·m-1.The estimated CST values of the adaxial and abaxial rice leaf surface were 29.90 and 31.22 mN·m-1，respectively.Among the measured Silwet-408 solutions，the droplets of solutions at lower concentrations(0，3.91，7.81 mg·L-1)rolled off rice leaf with different inclination angles on condition that their surface tensions were more than the CST of rice leaf and Silwet-408 concentrations were less than the CMC.Surface tensions of solutions at concentrations 15.63，31.25，and 62.50 mg·L-1 were less than the CST of rice leaf and Silwet-408 concentrations were less than the CMC.Droplets of solutions at concentrations 15.63 and 31.25 mg·L-1 adhered to rice leaf with lower inclination angle(30°).On the contrary，droplets rolled off rice leaf with higher inclination angle(60°).Droplets of solutions at 62.50 mg·L-1 adhered to rice leaf and significant differences existed in decreasing speed ofθvariation and wetting hysteresis.The droplets of solutions at higher concentrations of 125.00 and 250.00 mg·L-1 adhered to rice leaf with different inclination angles on condition that their surface tensions were less than the CST of rice leaf and Silwet-408 concentrations were more than the CMC.After 40 s，no significant differences were observed in decreasing speed ofθvariation and wetting hysteresis.Analysis results of advancing and receding angles on rice leaf surface with different inclination angles showed that advancing angles(θa)were larger than receding angles(θr).Within 40 s，bothθa andθr decreased gradually.[Conclusion]The higher hydrophobicity of rice leaf is mainly ascribed to densely covered wax papillae on rice leaf surface and it may be related to hair length and stomatal density of rice leaf.Rice leaf surface is low energy.When surface tensions of Silwet-408 solutions are less than the CST of rice leaf surface and the concentrations of Silwet-408 are more than the CMC，droplets would show better adhesion on rice leaf surface with different inclination angles and wetting.Because of larger surface tension，droplets of low concentration solutions on rice leaf surface with different inclination angles are easier to roll off.Thatθa of droplets of Silwet-408 solutions on rice leaf surface with different inclination angles are always larger thanθr illustrates wetting hysteresis.The phenomenon of wetting hysteresis indicates that rice leaf surface is rough and roughness is closely related to densely covered papillae on rice leaf surface.