徐廣春，顧中言(yan)，徐德進，許小龍(long)

目的(de)(de)(de)研究(jiu)水(shui)稻葉片(pian)(pian)的(de)(de)(de)表面(mian)(mian)特(te)性和有(you)機硅助(zhu)劑Silwet-408溶(rong)液的(de)(de)(de)單(dan)個霧(wu)滴在30°、45°和60°3個傾角(jiao)水(shui)稻葉片(pian)(pian)正、反面(mian)(mian)的(de)(de)(de)行為，以期(qi)為農(nong)藥霧(wu)滴對(dui)靶(ba)葉面(mian)(mian)滯(zhi)留控制(zhi)機制(zhi)提(ti)供依據。方法(fa)(fa)利用掃描(miao)電(dian)鏡觀察(cha)水(shui)稻葉片(pian)(pian)的(de)(de)(de)表面(mian)(mian)特(te)性，并通過Zisman圖(tu)法(fa)(fa)測(ce)定(ding)(ding)稻葉的(de)(de)(de)臨界表面(mian)(mian)張(zhang)力。同時(shi)測(ce)定(ding)(ding)0、3.91、7.81、15.63、31.25、62.50、125.00和250.00 mg·L-18個濃(nong)度(du)的(de)(de)(de)Silwet-408溶(rong)液的(de)(de)(de)表面(mian)(mian)張(zhang)力后，利用表面(mian)(mian)張(zhang)力法(fa)(fa)測(ce)定(ding)(ding)出(chu)Silwet-408的(de)(de)(de)臨界膠束(shu)濃(nong)度(du)，并借助(zhu)于接(jie)觸角(jiao)測(ce)量儀(yi)測(ce)定(ding)(ding)8個溶(rong)液的(de)(de)(de)單(dan)個霧(wu)滴在3個傾角(jiao)水(shui)稻葉片(pian)(pian)上的(de)(de)(de)接(jie)觸角(jiao)。

結(jie)果(guo)電鏡觀(guan)察(cha)發現水(shui)稻葉(xie)片(pian)(pian)正、反(fan)面(mian)(mian)存在(zai)3種類型的(de)(de)絨毛，同時表(biao)面(mian)(mian)布(bu)滿了乳頭(tou)狀的(de)(de)突起，其密度(du)(du)分別為(wei)（12.4±0.7）×103和(he)(he)（7.6±0.8）×103個/mm2且差異顯(xian)著；氣孔(kong)長度(du)(du)和(he)(he)氣孔(kong)密度(du)(du)間均無(wu)顯(xian)著差異。Silwet-408的(de)(de)臨(lin)界(jie)膠(jiao)束濃(nong)度(du)(du)為(wei)78.5 mg·L-1，與之相(xiang)對應的(de)(de)溶液(ye)的(de)(de)表(biao)面(mian)(mian)張力為(wei)20.77 mN·m-1。水(shui)稻葉(xie)片(pian)(pian)正、反(fan)面(mian)(mian)的(de)(de)臨(lin)界(jie)表(biao)面(mian)(mian)張力估值分別為(wei)29.90和(he)(he)31.22 mN·m-1。在(zai)所測定(ding)的(de)(de)溶液(ye)中，濃(nong)度(du)(du)為(wei)0、3.91、7.81 mg·L-1溶液(ye)的(de)(de)表(biao)面(mian)(mian)張力大于稻葉(xie)的(de)(de)臨(lin)界(jie)表(biao)面(mian)(mian)張力且Silwet-408濃(nong)度(du)(du)小(xiao)于臨(lin)界(jie)膠(jiao)束濃(nong)度(du)(du)，這(zhe)3個濃(nong)度(du)(du)溶液(ye)的(de)(de)霧(wu)滴(di)將直接(jie)從不同傾角水(shui)稻葉(xie)片(pian)(pian)上滾落。

濃度(du)為15.63、31.25、62.50 mg·L-1溶(rong)(rong)液的(de)表(biao)面(mian)張力小(xiao)于(yu)(yu)稻(dao)葉(xie)的(de)臨(lin)(lin)界(jie)表(biao)面(mian)張力且(qie)(qie)Silwet-408濃度(du)小(xiao)于(yu)(yu)臨(lin)(lin)界(jie)膠束濃度(du)，15.63和(he)31.25 mg·L-1溶(rong)(rong)液的(de)霧(wu)滴(di)在傾角(jiao)(jiao)(jiao)較低時(shi)（30°）能黏附葉(xie)片(pian)上(shang)，較高時(shi)（60°）滾落；62.50 mg·L-1溶(rong)(rong)液的(de)霧(wu)滴(di)能黏附在稻(dao)葉(xie)上(shang)，不同傾角(jiao)(jiao)(jiao)間(jian)的(de)接觸角(jiao)(jiao)(jiao)變(bian)化(hua)率和(he)潤濕(shi)滯后(hou)(hou)存(cun)在差異(yi)；125.00和(he)250.00 mg·L-1溶(rong)(rong)液的(de)表(biao)面(mian)張力小(xiao)于(yu)(yu)稻(dao)葉(xie)的(de)臨(lin)(lin)界(jie)表(biao)面(mian)張力且(qie)(qie)Silwet-408濃度(du)大(da)于(yu)(yu)臨(lin)(lin)界(jie)膠束濃度(du)，這2個溶(rong)(rong)液的(de)霧(wu)滴(di)均能黏附在不同傾角(jiao)(jiao)(jiao)的(de)水稻(dao)葉(xie)片(pian)上(shang)，40 s后(hou)(hou)的(de)接觸角(jiao)(jiao)(jiao)變(bian)化(hua)率和(he)潤濕(shi)滯后(hou)(hou)無顯著差異(yi)。不同傾角(jiao)(jiao)(jiao)稻(dao)葉(xie)上(shang)霧(wu)滴(di)的(de)前進角(jiao)(jiao)(jiao)（θa）和(he)后(hou)(hou)退角(jiao)(jiao)(jiao)（θr）的(de)分(fen)析(xi)結果(guo)表(biao)明(ming)θa總(zong)是大(da)于(yu)(yu)θr，在40 s的(de)測定(ding)時(shi)間(jian)內，隨(sui)時(shi)間(jian)延遲θa和(he)θr總(zong)是逐漸(jian)減少。

結論稻(dao)(dao)葉(xie)(xie)(xie)的(de)強疏水性(xing)主要歸因于(yu)其(qi)表(biao)(biao)(biao)面(mian)布滿了(le)包被(bei)著蠟質的(de)乳頭狀突起，同(tong)時這還可能與其(qi)葉(xie)(xie)(xie)表(biao)(biao)(biao)面(mian)的(de)毛長和氣孔(kong)密(mi)(mi)度(du)(du)密(mi)(mi)切相(xiang)關(guan)。水稻(dao)(dao)葉(xie)(xie)(xie)面(mian)為(wei)低能葉(xie)(xie)(xie)面(mian)。只有Silwet-408溶液的(de)表(biao)(biao)(biao)面(mian)張(zhang)力(li)小于(yu)稻(dao)(dao)葉(xie)(xie)(xie)的(de)臨界(jie)(jie)表(biao)(biao)(biao)面(mian)張(zhang)力(li)且溶液中的(de)Silwet-408濃(nong)度(du)(du)達到臨界(jie)(jie)膠束濃(nong)度(du)(du)才(cai)能使霧(wu)滴很(hen)好的(de)黏(nian)附(fu)在不同(tong)傾(qing)角(jiao)的(de)稻(dao)(dao)葉(xie)(xie)(xie)上(shang)并潤(run)濕展布；過(guo)低濃(nong)度(du)(du)的(de)溶液的(de)霧(wu)滴由(you)于(yu)較大的(de)表(biao)(biao)(biao)面(mian)張(zhang)力(li)易(yi)從不同(tong)傾(qing)角(jiao)的(de)稻(dao)(dao)葉(xie)(xie)(xie)上(shang)滾(gun)落(luo)。Silwet-408溶液的(de)霧(wu)滴在不同(tong)傾(qing)角(jiao)葉(xie)(xie)(xie)片(pian)上(shang)的(de)θa大于(yu)θr形成的(de)潤(run)濕滯(zhi)后說明了(le)稻(dao)(dao)葉(xie)(xie)(xie)表(biao)(biao)(biao)面(mian)的(de)粗糙(cao)，而這種粗糙(cao)與稻(dao)(dao)葉(xie)(xie)(xie)表(biao)(biao)(biao)面(mian)存在的(de)高密(mi)(mi)度(du)(du)乳突密(mi)(mi)切相(xiang)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.