徐廣春(chun)，顧中(zhong)言，徐德進，許小龍

目的(de)研究(jiu)水稻(dao)(dao)葉片(pian)的(de)表(biao)面(mian)特性(xing)和(he)(he)有機硅助(zhu)劑Silwet-408溶液的(de)單個(ge)(ge)(ge)(ge)霧滴(di)(di)在(zai)(zai)30°、45°和(he)(he)60°3個(ge)(ge)(ge)(ge)傾(qing)角(jiao)水稻(dao)(dao)葉片(pian)正、反面(mian)的(de)行為，以期為農藥霧滴(di)(di)對靶葉面(mian)滯(zhi)留(liu)控(kong)制機制提供依據。方法(fa)利用(yong)掃描電鏡觀察(cha)水稻(dao)(dao)葉片(pian)的(de)表(biao)面(mian)特性(xing)，并(bing)(bing)通過(guo)Zisman圖法(fa)測(ce)定(ding)稻(dao)(dao)葉的(de)臨(lin)界表(biao)面(mian)張力(li)。同時測(ce)定(ding)0、3.91、7.81、15.63、31.25、62.50、125.00和(he)(he)250.00 mg·L-18個(ge)(ge)(ge)(ge)濃度的(de)Silwet-408溶液的(de)表(biao)面(mian)張力(li)后，利用(yong)表(biao)面(mian)張力(li)法(fa)測(ce)定(ding)出(chu)Silwet-408的(de)臨(lin)界膠束(shu)濃度，并(bing)(bing)借助(zhu)于接觸角(jiao)測(ce)量(liang)儀測(ce)定(ding)8個(ge)(ge)(ge)(ge)溶液的(de)單個(ge)(ge)(ge)(ge)霧滴(di)(di)在(zai)(zai)3個(ge)(ge)(ge)(ge)傾(qing)角(jiao)水稻(dao)(dao)葉片(pian)上的(de)接觸角(jiao)。

結果電鏡觀察發現水稻(dao)葉片正、反(fan)面(mian)(mian)(mian)存在3種(zhong)類(lei)型的(de)絨(rong)毛(mao)，同時表面(mian)(mian)(mian)布滿(man)了乳頭狀的(de)突起(qi)，其密度(du)(du)(du)分別為（12.4±0.7）×103和（7.6±0.8）×103個(ge)/mm2且差異顯(xian)著；氣(qi)孔(kong)長度(du)(du)(du)和氣(qi)孔(kong)密度(du)(du)(du)間(jian)均無顯(xian)著差異。Silwet-408的(de)臨(lin)界(jie)膠束濃(nong)度(du)(du)(du)為78.5 mg·L-1，與之相對應的(de)溶液(ye)(ye)的(de)表面(mian)(mian)(mian)張(zhang)力(li)為20.77 mN·m-1。水稻(dao)葉片正、反(fan)面(mian)(mian)(mian)的(de)臨(lin)界(jie)表面(mian)(mian)(mian)張(zhang)力(li)估值分別為29.90和31.22 mN·m-1。在所(suo)測(ce)定的(de)溶液(ye)(ye)中，濃(nong)度(du)(du)(du)為0、3.91、7.81 mg·L-1溶液(ye)(ye)的(de)表面(mian)(mian)(mian)張(zhang)力(li)大于(yu)稻(dao)葉的(de)臨(lin)界(jie)表面(mian)(mian)(mian)張(zhang)力(li)且Silwet-408濃(nong)度(du)(du)(du)小于(yu)臨(lin)界(jie)膠束濃(nong)度(du)(du)(du)，這3個(ge)濃(nong)度(du)(du)(du)溶液(ye)(ye)的(de)霧滴(di)將直接從(cong)不同傾角水稻(dao)葉片上滾(gun)落。

濃(nong)度為15.63、31.25、62.50 mg·L-1溶(rong)(rong)液(ye)(ye)的(de)(de)(de)表(biao)(biao)(biao)面張力小(xiao)(xiao)于(yu)(yu)稻(dao)(dao)(dao)葉(xie)(xie)(xie)的(de)(de)(de)臨界(jie)表(biao)(biao)(biao)面張力且(qie)Silwet-408濃(nong)度小(xiao)(xiao)于(yu)(yu)臨界(jie)膠(jiao)束濃(nong)度，15.63和(he)(he)31.25 mg·L-1溶(rong)(rong)液(ye)(ye)的(de)(de)(de)霧(wu)滴(di)在傾(qing)角較低(di)時(shi)(shi)（30°）能(neng)黏(nian)(nian)附葉(xie)(xie)(xie)片上(shang)，較高時(shi)(shi)（60°）滾落；62.50 mg·L-1溶(rong)(rong)液(ye)(ye)的(de)(de)(de)霧(wu)滴(di)能(neng)黏(nian)(nian)附在稻(dao)(dao)(dao)葉(xie)(xie)(xie)上(shang)，不(bu)同傾(qing)角間(jian)的(de)(de)(de)接(jie)觸角變(bian)(bian)化(hua)率(lv)和(he)(he)潤濕(shi)滯后(hou)(hou)存在差異；125.00和(he)(he)250.00 mg·L-1溶(rong)(rong)液(ye)(ye)的(de)(de)(de)表(biao)(biao)(biao)面張力小(xiao)(xiao)于(yu)(yu)稻(dao)(dao)(dao)葉(xie)(xie)(xie)的(de)(de)(de)臨界(jie)表(biao)(biao)(biao)面張力且(qie)Silwet-408濃(nong)度大于(yu)(yu)臨界(jie)膠(jiao)束濃(nong)度，這2個溶(rong)(rong)液(ye)(ye)的(de)(de)(de)霧(wu)滴(di)均能(neng)黏(nian)(nian)附在不(bu)同傾(qing)角的(de)(de)(de)水稻(dao)(dao)(dao)葉(xie)(xie)(xie)片上(shang)，40 s后(hou)(hou)的(de)(de)(de)接(jie)觸角變(bian)(bian)化(hua)率(lv)和(he)(he)潤濕(shi)滯后(hou)(hou)無顯(xian)著差異。不(bu)同傾(qing)角稻(dao)(dao)(dao)葉(xie)(xie)(xie)上(shang)霧(wu)滴(di)的(de)(de)(de)前進(jin)角（θa）和(he)(he)后(hou)(hou)退角（θr）的(de)(de)(de)分析結(jie)果表(biao)(biao)(biao)明θa總是(shi)大于(yu)(yu)θr，在40 s的(de)(de)(de)測定時(shi)(shi)間(jian)內，隨時(shi)(shi)間(jian)延遲θa和(he)(he)θr總是(shi)逐漸減(jian)少。

結論稻(dao)葉(xie)(xie)(xie)(xie)的(de)(de)(de)強疏(shu)水(shui)性主要歸因(yin)于(yu)其表(biao)面(mian)(mian)布(bu)滿了包被(bei)著(zhu)蠟質的(de)(de)(de)乳(ru)(ru)頭狀突起，同(tong)時這(zhe)還(huan)可能與其葉(xie)(xie)(xie)(xie)表(biao)面(mian)(mian)的(de)(de)(de)毛長(chang)和氣孔密(mi)度(du)密(mi)切(qie)相關。水(shui)稻(dao)葉(xie)(xie)(xie)(xie)面(mian)(mian)為低能葉(xie)(xie)(xie)(xie)面(mian)(mian)。只有Silwet-408溶(rong)液的(de)(de)(de)表(biao)面(mian)(mian)張(zhang)力(li)(li)小于(yu)稻(dao)葉(xie)(xie)(xie)(xie)的(de)(de)(de)臨界(jie)表(biao)面(mian)(mian)張(zhang)力(li)(li)且(qie)溶(rong)液中的(de)(de)(de)Silwet-408濃(nong)度(du)達到臨界(jie)膠束濃(nong)度(du)才能使霧(wu)滴(di)(di)很好的(de)(de)(de)黏附在不(bu)(bu)同(tong)傾(qing)角(jiao)的(de)(de)(de)稻(dao)葉(xie)(xie)(xie)(xie)上(shang)并潤濕展(zhan)布(bu)；過低濃(nong)度(du)的(de)(de)(de)溶(rong)液的(de)(de)(de)霧(wu)滴(di)(di)由于(yu)較大的(de)(de)(de)表(biao)面(mian)(mian)張(zhang)力(li)(li)易從不(bu)(bu)同(tong)傾(qing)角(jiao)的(de)(de)(de)稻(dao)葉(xie)(xie)(xie)(xie)上(shang)滾落。Silwet-408溶(rong)液的(de)(de)(de)霧(wu)滴(di)(di)在不(bu)(bu)同(tong)傾(qing)角(jiao)葉(xie)(xie)(xie)(xie)片上(shang)的(de)(de)(de)θa大于(yu)θr形成的(de)(de)(de)潤濕滯后說明了稻(dao)葉(xie)(xie)(xie)(xie)表(biao)面(mian)(mian)的(de)(de)(de)粗糙(cao)，而這(zhe)種(zhong)粗糙(cao)與稻(dao)葉(xie)(xie)(xie)(xie)表(biao)面(mian)(mian)存在的(de)(de)(de)高密(mi)度(du)乳(ru)(ru)突密(mi)切(qie)相關。

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.