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烷基聚葡糖苷液滴在黃瓜葉面的潤(rùn)濕狀態(tài)及動(dòng)態(tài)鋪展行為

2017-03-04 03:01:14張紅濤魏德云胡玉霞
關(guān)鍵詞:表面張力葉面液滴

張紅濤,陸 軍,魏德云,胡玉霞

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烷基聚葡糖苷液滴在黃瓜葉面的潤(rùn)濕狀態(tài)及動(dòng)態(tài)鋪展行為

張紅濤1,陸 軍2※,魏德云2,胡玉霞3

(1. 華北水利水電大學(xué)電力學(xué)院,鄭州 450011;2. 浙江農(nóng)林大學(xué)暨陽學(xué)院,諸暨311800;3. 鄭州大學(xué)電氣工程學(xué)院,鄭州 450001)

為了探究烷基聚葡糖苷(alkyl polyglycosid,APG)在黃瓜葉面的動(dòng)態(tài)潤(rùn)濕行為及其動(dòng)態(tài)接觸角變化規(guī)律,采用表面張力與接觸角測(cè)量?jī)x測(cè)量了一次去離子水和9種質(zhì)量百分?jǐn)?shù)APG水溶液(14.35%~85.78%)的表面張力、液滴葉面接觸角與動(dòng)態(tài)接觸角、前進(jìn)角與后退角、鋪展直徑等動(dòng)態(tài)潤(rùn)濕參數(shù)。依據(jù)Tanner法則對(duì)接觸角滯后現(xiàn)象、鋪展驅(qū)動(dòng)力成因進(jìn)行分析和推測(cè),并應(yīng)用冪次法則擬合了鋪展直徑與冪值和時(shí)間的關(guān)系曲線。結(jié)果表明,9種APG水溶液的表面張力介于27.96~29.73 mN/m小幅范圍內(nèi),而接觸角卻在11.35°~34.20°較大范圍內(nèi)變化;接觸角滯后性(Δ=46.89°)較大,反映出一次去離子水在活體植物黃瓜葉面的接觸角變化符合粗糙表面上接觸角滯后現(xiàn)象的基本規(guī)律;各質(zhì)量百分?jǐn)?shù)APG溶液的動(dòng)態(tài)接觸角在前1 s內(nèi)急速下降,在之后1~10 s平穩(wěn)減小并漸趨于穩(wěn)定;APG在黃瓜葉面的鋪展直徑與時(shí)間的關(guān)系均較好地符合冪次法則,據(jù)此推測(cè)動(dòng)態(tài)表面張力是黃瓜葉面(界面)占據(jù)絕對(duì)優(yōu)勢(shì)的鋪展驅(qū)動(dòng)力。

接觸角;潤(rùn)濕;液滴;烷基聚葡糖苷,黃瓜葉片,動(dòng)態(tài)潤(rùn)濕,Tanner法則

0 引 言

改善藥液在靶標(biāo)表面的潤(rùn)濕性是提高農(nóng)藥利用率的有效途徑之一。噴霧藥液到達(dá)靶標(biāo)植株后,會(huì)在其表面發(fā)生沉積、持留、鋪展和滲透[1-3]等系列動(dòng)態(tài)過程,其中霧滴著靶動(dòng)態(tài)潤(rùn)濕行為將直接影響施藥效果,并決定藥液向生物體的傳遞規(guī)律。21世紀(jì)后,藥液與靶標(biāo)界面的動(dòng)態(tài)潤(rùn)濕行為研究,已成為農(nóng)藥應(yīng)用技術(shù)領(lǐng)域非?;钴S的研究方向[4-7],也是精準(zhǔn)施藥技術(shù)重要的研究?jī)?nèi)容之一[8-10]。

不同植物葉片表面特征決定其潤(rùn)濕性的差異,一般易濕潤(rùn)葉面是指水滴在其表面的接觸角小于110°的葉片,而難濕潤(rùn)葉面是指大于110°的葉片[11-12]。精準(zhǔn)施藥技術(shù)要求噴霧藥液到達(dá)植株靶標(biāo)葉面后迅速鋪展,根據(jù)霧滴藥液的動(dòng)態(tài)表面張力值和動(dòng)態(tài)接觸角來篩選農(nóng)藥助劑[13-15]。

作為國(guó)際公認(rèn)的首選“綠色”功能性表面活性劑-烷基聚葡糖苷(alkyl polyglycosid,APG),因其具有高表面活性和生態(tài)安全性而備受關(guān)注。近年來圍繞APG農(nóng)藥助劑制備、改性及其增效作用機(jī)制研究,國(guó)內(nèi)外學(xué)者作了大量的工作,并取得了較為明顯的成果[16-18]。如Holloway等[19-21]研究了在農(nóng)藥藥液中添加APG等表面活性劑以減小藥液表面張力及藥液葉片表面接觸角的方法;王波等[22]研究了劑型及表面活性劑對(duì)農(nóng)藥藥液在植物葉片上鋪展行為的影響,試驗(yàn)結(jié)果表明表面張力并非增強(qiáng)藥液持留和鋪展能力的唯一因素;王淑杰等[23]研究了典型植物葉片對(duì)農(nóng)藥潤(rùn)濕特性及持藥量的影響,結(jié)果表明植物葉片的潤(rùn)濕性與藥液持留量有一定相關(guān)性,兩者都受葉面表面特征的影響,同時(shí)藥液持留量還受葉片對(duì)藥液黏附性影響。但在精準(zhǔn)施藥技術(shù)領(lǐng)域動(dòng)態(tài)潤(rùn)濕方面的研究報(bào)道卻相對(duì)較少[24-25]。

本文擬通過測(cè)量9種APG水溶液的表面張力,以及APG液滴在黃瓜葉片表面的動(dòng)態(tài)接觸角、鋪展直徑等動(dòng)態(tài)潤(rùn)濕參數(shù),探討APG在活體植物黃瓜葉面接觸角變化及滯后現(xiàn)象的基本規(guī)律,研究其鋪展特性及驅(qū)動(dòng)力成因,為以黃瓜為靶標(biāo)、APG為助劑的農(nóng)藥噴施提供理論依據(jù)和技術(shù)支持。

1 材料與方法

1.1 材料與儀器

烷基聚葡糖苷(試劑型號(hào)APG-0810,南京金陵石化研究院,由該廠家提供的產(chǎn)品技術(shù)指標(biāo)為:烷基碳數(shù)8~10、活性物50.0%、糖聚合度1.6~1.8、殘留醇≤1%、HLB值15~16、pH值11.5~12.5);新鮮黃瓜葉片(黃瓜品種為津研4號(hào),溫室生長(zhǎng)65 d,從頂端向下第4片葉子,為保持葉片新鮮,均在采摘后2 h內(nèi)進(jìn)行試驗(yàn))。

表面張力與接觸角測(cè)量?jī)x(KSV CAM 101型,芬蘭KSV儀器公司),該儀器主要參數(shù)和技術(shù)指標(biāo)如表1所示;微量注射器(量程0.5~100L,瑞士Hamilton公司)。

表1 KSV測(cè)量?jī)x的技術(shù)參數(shù)

1.2 試驗(yàn)方案

由于采用的烷基聚葡糖苷(APG-0810)不是工業(yè)提純的表面活性劑,試驗(yàn)配置了包含低(10~29%)、中(30~69%)、高(70~89%)濃度在內(nèi)的9種APG水溶液作為液滴試劑。實(shí)驗(yàn)室環(huán)境溫度(3±1)℃,濕度58%±2%。首先用一次去離子水與APG試劑配制9種濃度的APG水溶液,質(zhì)量百分?jǐn)?shù)分別為14.35%、20.08%、25.09%、33.44%、50.12%、66.78%、75.09%、80.08%、85.78%(均在配制后2 h內(nèi)進(jìn)行試驗(yàn))。沿著黃瓜葉片中部主葉脈對(duì)稱剪下2.5 cm×2.5 cm的部分作為試驗(yàn)樣本,平整鋪放在載玻片上[2,14]。從微量注射器中旋出5~10L上述各種濃度的液滴,分別滴于載玻片黃瓜葉片樣本上。采用懸滴法測(cè)定各濃度體系A(chǔ)PG水溶液的表面張力,再采用躺滴法測(cè)量接觸角、動(dòng)態(tài)接觸角、前進(jìn)角、后退角、鋪展直徑等動(dòng)態(tài)潤(rùn)濕參數(shù),KSV表面張力與接觸角測(cè)量?jī)x用自帶的CCD攝像機(jī)采集圖像數(shù)據(jù),利用CAM 2008圖像分析軟件進(jìn)行液滴形狀分析和輪廓擬合,由此測(cè)出上述表面張力值和動(dòng)態(tài)潤(rùn)濕參數(shù)值。依據(jù)前期觀測(cè)和預(yù)試驗(yàn),圖像采集時(shí)間設(shè)置在2~16 s內(nèi),圖像采集速率分別設(shè)定為62.50、10.42和8.93 幀/s。每種濃度體系的液滴重復(fù)試驗(yàn)3次,測(cè)試結(jié)果取平均值。

1.3 測(cè)量方法

1.3.1 表面張力的測(cè)量方法

用懸滴法測(cè)量表面張力。從微量注射器的平底針口處旋出5~10L液滴,在懸滴狀態(tài)下保持2 min以上使液滴趨于平穩(wěn),CCD攝像機(jī)在靜態(tài)模式下采集圖像,由圖像輪廓擬合結(jié)果測(cè)量出表面張力,懸滴圖像及其擬合如圖1a~b所示。

圖1 液滴圖像及其擬合圖像

1.3.2 接觸角、動(dòng)態(tài)接觸角θ的測(cè)量方法

躺滴法測(cè)量接觸角、動(dòng)態(tài)接觸角θ。液滴落下角度不同,在到達(dá)葉面并接觸瞬間,其滴型形狀會(huì)有明顯不同,會(huì)直接影響接觸角的測(cè)量,因此本文接觸角、動(dòng)態(tài)接觸角測(cè)量全部采用垂直滴落方式。以垂直自由落體的方式,從微量注射器的平底針口處旋出5~10L液滴,滴于黃瓜葉片表面,微量注射器平底針口距離黃瓜葉片表面6.8 cm。液滴在葉面自由動(dòng)態(tài)鋪展2 min,液滴趨于平穩(wěn)后,CCD攝像機(jī)在靜態(tài)模式下采集圖像,由圖像輪廓擬合結(jié)果測(cè)量出接觸角。上述過程CCD攝像機(jī)在連續(xù)記錄模式下以62.50幀/s的速度采集圖像,圖像采集時(shí)間2 s,連續(xù)的每幀圖像輪廓擬合結(jié)果測(cè)量出動(dòng)態(tài)接觸角,躺滴圖像及其擬合如圖1c~d所示。

1.3.3 鋪展直徑的測(cè)量方法

調(diào)整微量注射器使其平底針口與載玻片上黃瓜葉面距離6.8 cm,再從微量注射器的平底針口處旋出5~10L液滴,以垂直自由落體的方式,滴于黃瓜葉片表面。設(shè)置圖像采集時(shí)間10 s,圖像采集速率設(shè)定8.93幀/s,由圖像輪廓擬合測(cè)量出動(dòng)態(tài)鋪展直徑,鋪展直徑圖像及其擬合如圖1e~f所示。

1.3.4 前進(jìn)角θ、后退角θ的測(cè)量方法

從微量注射器平底針口旋出5~10L液滴滴于黃瓜葉面,再以很低的速度加入(或移走)液滴,不斷增大(或減?。┰撘旱误w積,在此移動(dòng)過程初期,液滴與葉面的接觸角逐漸增大(或減?。?,而接觸面積并不發(fā)生變化。但當(dāng)液滴的體積達(dá)到臨界值時(shí),液滴在葉面的三相接觸線則發(fā)生往外(或往里)移動(dòng)。設(shè)置圖像采集時(shí)間10 s,圖像采集速率設(shè)定10.42幀/s,在連續(xù)模式下用CCD攝像機(jī)記錄上述過程到達(dá)臨界值發(fā)生移動(dòng)前變化的接觸角,即為所測(cè)量的前進(jìn)角(或后退角)。測(cè)量過程中前進(jìn)角θ(或后退角θ)的摩擦方向及其圖像輪廓擬合,如圖2所示。

圖2 前進(jìn)角與后退角的測(cè)量

1.4 研究方法

Tanner法則[26]認(rèn)為,對(duì)于通過在固、氣、液三相線處非平衡表(界)面張力導(dǎo)致的鋪展,其鋪展直徑與時(shí)間的關(guān)系符合以下關(guān)系,即

Tanner法則中[26-27],當(dāng)表面張力為時(shí)間的函數(shù)時(shí),推出冪值<0.1的情況;當(dāng)鋪展直徑隨時(shí)間變化呈線性關(guān)系時(shí),符合最大鋪展速度條件下完全由表面張力梯度導(dǎo)致的超鋪展行為,推出冪值=1的情況,即()∝·;當(dāng)液體黏度、表面張力、液滴體積均變化很小或趨于穩(wěn)定且相對(duì)恒定時(shí),符合三相線處非平衡表(界)面張力導(dǎo)致的鋪展行為,推出冪值=0.1的情況,即()∝·0.1。

2 結(jié)果與分析

2.1 不同質(zhì)量百分?jǐn)?shù)APG的表面張力

試驗(yàn)首先測(cè)量了一次去離子水和APG液滴的表面張力值,分別為71.16和30.73 mN/m。而APG水溶液的表面張力與濃度密切關(guān)聯(lián),重復(fù)3次測(cè)量與平均值相比,正負(fù)偏差小于5%的APG水溶液表面張力值隨濃度(質(zhì)量百分?jǐn)?shù))變化的關(guān)系,如圖3所示。從圖3可以看出,質(zhì)量百分?jǐn)?shù)為14.35%~33.44%的APG水溶液的表面張力值變化范圍在29.73~29.08 mN/m內(nèi),呈略微減少趨勢(shì)。而質(zhì)量百分?jǐn)?shù)為50.12%~80.08%的APG水溶液的表面張力值變化不大,范圍在28.90~28.27 mN/m之間。隨著濃度的增加,當(dāng)APG質(zhì)量百分?jǐn)?shù)達(dá)到85.78%時(shí),溶液的表面張力值降至27.96 mN/m,是所配制9種濃度APG水溶液表面張力值中的最小值。

注:APG,為烷基聚葡糖苷。下同。

2.2 黃瓜葉面接觸角、動(dòng)態(tài)接觸角

9種質(zhì)量百分?jǐn)?shù)的APG水溶液液滴的黃瓜葉面接觸角值如圖3所示。從圖3可以看出,隨著質(zhì)量百分?jǐn)?shù)濃度的增加,黃瓜葉面接觸角呈單峰曲線變化趨勢(shì),最小值為11.35°,在APG質(zhì)量百分?jǐn)?shù)為66.78%時(shí)接觸角達(dá)到最大峰值34.20°。

在16 s內(nèi)APG液滴、一次去離子水液滴的黃瓜葉面動(dòng)態(tài)接觸角θ值如圖4所示。由圖4可以看出,前2 s內(nèi)APG液滴動(dòng)態(tài)接觸角θ值急劇減小,在之后2~16 s內(nèi)逐漸趨于穩(wěn)定。APG液滴前2 s鋪展速率極大,雖然動(dòng)態(tài)接觸角θ的理論最大初始值為180°,但試驗(yàn)所能測(cè)到的最大動(dòng)態(tài)接觸角θ(當(dāng)→0時(shí)的初始值)為102.37°,在趨于平穩(wěn)后測(cè)到的動(dòng)態(tài)接觸角θ(當(dāng)→16 s時(shí)的穩(wěn)定值)為29.47°,動(dòng)態(tài)接觸角減小的幅度達(dá)到72.90°。而在16 s內(nèi)一次去離子水液滴的動(dòng)態(tài)接觸θ值變化極小,滴于葉面后相對(duì)穩(wěn)定在94.30°~94.70°范圍內(nèi)。

圖4 一次去離子水和APG試劑在黃瓜葉片上的動(dòng)態(tài)接觸角

9種質(zhì)量百分?jǐn)?shù)的APG水溶液液滴的黃瓜葉面動(dòng)態(tài)接觸角θ值如圖5所示。從圖5可看出,9種質(zhì)量百分?jǐn)?shù)APG液滴在黃瓜葉面的動(dòng)態(tài)接觸角θ均在前1 s內(nèi)急速減小,在之后1~10 s逐漸趨于穩(wěn)定。在可觀測(cè)的前1 s內(nèi),質(zhì)量百分?jǐn)?shù)為25.09%的APG液滴,其動(dòng)態(tài)接觸角減小幅度達(dá)到36.73%。APG液滴在黃瓜葉面的動(dòng)態(tài)接觸角θ隨著時(shí)間增加而減小,主要有2方面的影響因素,一是液滴表面張力的變化,二是接觸角的滯后效應(yīng)。9種濃度APG液滴的黃瓜葉面動(dòng)態(tài)接觸角θ值變化幅度較大,但它們的表面張力值卻在27.96~29.73 mN/m較窄的范圍內(nèi),可以推測(cè)9種濃度APG液滴在黃瓜葉面的潤(rùn)濕性能可能與其表(界)面張力的動(dòng)態(tài)行為有關(guān)。

圖5 不同質(zhì)量百分?jǐn)?shù)APG液滴黃瓜葉面動(dòng)態(tài)接觸角

2.3 黃瓜葉面前進(jìn)角、后退角

10 s內(nèi)一次去離子水在黃瓜葉面的前進(jìn)角θ與后退角θ,如圖6所示。由圖6可看出,隨著時(shí)間的增加,一次去離子水在黃瓜葉面上的前進(jìn)角θ增大,后退接觸角θ減小。在10 s內(nèi)前進(jìn)角增加7.54°,而后退角減小22.85°,即10 s內(nèi)前進(jìn)角增大幅度小于后退角減小幅度。黃瓜葉片表面的接觸角滯后性(Δ=46.89°)較大。根據(jù)文獻(xiàn)[28],圖9的試驗(yàn)數(shù)據(jù)反映出,一次去離子水在活體植物黃瓜葉面的接觸角變化符合粗糙表面上接觸角滯后現(xiàn)象的基本規(guī)律。

圖6 一次去離子水在黃瓜葉片上的前進(jìn)角與后退角

2.4 黃瓜葉面鋪展直徑

APG試劑液滴在黃瓜葉面0.35 s內(nèi)的鋪展圖像,如圖7所示。從圖7觀測(cè)可知,APG液滴展現(xiàn)出極好的潤(rùn)濕性能,液滴在接觸葉面瞬間就迅速鋪展開來。APG液滴在0.35 s內(nèi)的動(dòng)態(tài)接觸角由102.37°減小至56.53°,減小幅度達(dá)44.78%。

一次去離子水、APG試劑,以及低(25.09%)、中(66.78%)、高(75.09%)3種質(zhì)量百分?jǐn)?shù)APG液滴在黃瓜葉面10 s內(nèi)的鋪展直徑如圖8所示。從圖8可以看到,10 s內(nèi)一次去離子水液滴的黃瓜葉面鋪展直徑變化極小,其數(shù)據(jù)點(diǎn)連線幾乎接近于直線。而APG液滴的黃瓜葉面鋪展直徑均有不同程度的增加,在前1 s內(nèi)鋪展直徑增幅變化較大,之后1~9 s內(nèi)則變化相對(duì)平緩。此外,低質(zhì)量分?jǐn)?shù)(25.09%)APG液滴與APG試劑的變化趨勢(shì)相一致,而中(66.78%)和高(75.09%)質(zhì)量分?jǐn)?shù)APG液滴鋪展直徑隨著時(shí)間的增加,出現(xiàn)了短暫減小,特別在0.2~2 s內(nèi)減小較為明顯。據(jù)此推測(cè)APG液滴在鋪展過程中遇到葉面茸毛的阻礙作用,或受到葉脈脈絡(luò)的阻擋,使其鋪展過程造成短暫回流,該現(xiàn)象與黃瓜葉面結(jié)構(gòu)特征密切關(guān)聯(lián)[2]。

a. 0.05 s時(shí)的圖像a. Image at 0.05 sb. 0.08 s時(shí)的圖像b. Image at 0.08 s c. 0.11 s時(shí)的圖像c. Image at 0.11 sd. 0.14 s時(shí)的圖像d. Image at 0.14 s e. 0.18 s時(shí)的圖像e. Image at 0.18 sf. 0.35 s時(shí)的圖像f. Image at 0.35 s

圖8 一次去離子水和不同質(zhì)量百分?jǐn)?shù)APG溶液在黃瓜葉面的鋪展直徑

2.5 鋪展直徑與冪值和時(shí)間的關(guān)系

根據(jù)Tanner法則關(guān)于鋪展直徑與冪值和時(shí)間的關(guān)系,試驗(yàn)采集時(shí)間選取0~10 s,常數(shù)項(xiàng)設(shè)定=1,利用MATLAB軟件繪制出鋪展直徑隨冪值和時(shí)間變化的關(guān)系圖,如圖9所示。

在Tanner法則中,冪值介于0.01~0.1時(shí)的關(guān)系曲面如圖9a所示,冪值=0.1時(shí)的關(guān)系曲線如圖9b所示,冪值介于0.1~1時(shí)的關(guān)系曲面如圖9c所示。依據(jù)上述3種假定關(guān)系,試驗(yàn)測(cè)量發(fā)現(xiàn):鋪展直徑與時(shí)間的關(guān)系符合按() =·t的曲線擬合規(guī)律,即遵循冪次法則,根據(jù)Tanner法則關(guān)于鋪展直徑與冪值和時(shí)間的關(guān)系,通過擬合曲線,可以得到系列的系數(shù)值、冪值[2,27]。

上述現(xiàn)象可解釋為,各質(zhì)量百分?jǐn)?shù)APG液滴的黃瓜葉面鋪展過程不斷產(chǎn)生出新的表(界)面,在此過程中表面活性劑APG需要從體相不斷擴(kuò)散并吸附到新的表(界)面,由此各質(zhì)量百分?jǐn)?shù)APG在鋪展過程中的表面張力為動(dòng)態(tài)變化,且應(yīng)大于平衡表面張力[27]。測(cè)量結(jié)果遵循冪次法則[26],據(jù)此推測(cè):各質(zhì)量百分?jǐn)?shù)APG液滴的黃瓜葉面鋪展行為既不是由表面張力梯度導(dǎo)致,也不是由三相線處的非平衡表(界)面張力驅(qū)動(dòng)導(dǎo)致,而主要是由各質(zhì)量百分?jǐn)?shù)APG濃度體系的動(dòng)態(tài)表面張力變化引起的[2]。

圖9 鋪展直徑與冪值和時(shí)間的關(guān)系曲面及曲線

2.6 鋪展直徑擬合曲線

根據(jù)冪次法則,應(yīng)用MATLAB軟件對(duì)鋪展直徑數(shù)據(jù)點(diǎn)進(jìn)行曲線擬合。各質(zhì)量百分?jǐn)?shù)APG液滴黃瓜葉面鋪展直徑的擬合參數(shù)值及其曲線如表2所示。從表2可以看出,各質(zhì)量百分?jǐn)?shù)APG液滴黃瓜葉面擬合曲線的冪值在0.01~0.08范圍內(nèi),系數(shù)值的范圍在2.787 3~3.567 3之間,且低濃度APG呈現(xiàn)出較高的擬合程度。此外,質(zhì)量百分?jǐn)?shù)低于66.78%的APG,其冪值隨著濃度的增加而減小。根據(jù)文獻(xiàn)[26-28],冪次法則擬合結(jié)果反映出在黃瓜葉面鋪展過程中APG液滴的表面張力值是動(dòng)態(tài)變化的,該值應(yīng)大于平衡時(shí)的表面張力值,由此也推測(cè)出APG液滴黃瓜葉面的動(dòng)態(tài)表面張力是占據(jù)絕對(duì)優(yōu)勢(shì)的鋪展驅(qū)動(dòng)力,該動(dòng)態(tài)表面張力可視為引起鋪展的主導(dǎo)因素。

選取低(25.09%)、中(66.78%)2種質(zhì)量百分?jǐn)?shù)APG液滴與APG試劑(100%)液滴在黃瓜葉面10 s內(nèi)鋪展直徑的實(shí)測(cè)數(shù)據(jù)及其擬合曲線圖,如圖10所示。從圖10可以看出,無論濃度高低,這3種APG液滴的黃瓜葉面鋪展直徑都在前0.5 s內(nèi)急速增加,且鋪展速率(鋪展直徑/時(shí)間)幾乎相等。之后0.5~10 s內(nèi)鋪展直徑緩慢增加并各自趨于一個(gè)穩(wěn)定值,在趨于穩(wěn)定的過程中低濃度APG(25.09%)液滴與APG試劑(100%)的鋪展直徑變化幅度較大且穩(wěn)定值近似相等,而中濃度APG(66.78%)液滴的鋪展直徑變化幅度較小且穩(wěn)定值也最小。說明在黃瓜葉面低濃度APG(25.09%)就已經(jīng)能夠達(dá)到APG試劑(100%)的鋪展效果,配制低濃度的APG助劑即可滿足黃瓜葉片噴灑需要。APG液滴在黃瓜葉面鋪展過程中動(dòng)態(tài)表面張力變化程度決定其潤(rùn)濕性能及其作用,還需再根據(jù)葉面結(jié)構(gòu)特征和農(nóng)藥理化性質(zhì)配制適合的濃度。

表2 不同質(zhì)量百分?jǐn)?shù)APG溶液在黃瓜葉面上鋪展直徑的擬合曲線及其參數(shù)值

注:,鋪展直徑;,鋪展時(shí)間。

Note:, spreading diameter;, spreading time.

圖10 不同質(zhì)量百分?jǐn)?shù)APG溶液在黃瓜葉面上鋪展直徑的擬合曲線

3 結(jié) 論

1)質(zhì)量百分?jǐn)?shù)為14.35%~85.78%的9種APG溶液液滴試驗(yàn)樣本的表面張力值介于27.96~29.73 mN/m的較窄范圍內(nèi),但葉面接觸角卻介于11.35°~34.20°較寬范圍內(nèi),接觸角并沒有隨著濃度的增大而加劇變化。由此推測(cè)濃度并非影響接觸角變化的主導(dǎo)因素,黃瓜葉面的潤(rùn)濕性能與APG液滴的表(界)面張力及其動(dòng)態(tài)鋪展行為關(guān)聯(lián)密切。

2)作為一種易濕潤(rùn)葉面,10 s內(nèi)黃瓜葉片表面一次去離子水液滴的前進(jìn)角θ增加7.54°、后退角r減小22.85°,接觸角滯后性Δ=46.89°,說明一次去離子水液滴在活體植物黃瓜葉片表面的動(dòng)態(tài)潤(rùn)濕過程中,其表(界)面行為反映出葉面接觸角的變化符合粗糙表面接觸角滯后現(xiàn)象的基本規(guī)律。

3)不同質(zhì)量百分?jǐn)?shù)APG水溶液液滴在黃瓜葉面的鋪展直徑與時(shí)間的關(guān)系均較好地遵循Tanner 法則,即符合表面張力為時(shí)間的函數(shù)時(shí),冪值小于0.1的情況。各濃度體系A(chǔ)PG擬合曲線的冪值在0.01~0.08范圍內(nèi),系數(shù)值介于2.787 3~3.567 3之間,低濃度APG液滴的擬合程度較高。依據(jù)Tanner法則,推測(cè)出APG液滴黃瓜葉面的動(dòng)態(tài)表面張力是占據(jù)絕對(duì)優(yōu)勢(shì)的鋪展驅(qū)動(dòng)力。此外,作為活體植物靶標(biāo),黃瓜葉片的動(dòng)態(tài)鋪展并沒有隨APG溶液表面張力的下降而增強(qiáng),未來的研究需要采用電子顯微鏡深入觀察黃瓜葉片表面微觀結(jié)構(gòu),利用APG液滴動(dòng)態(tài)潤(rùn)濕行為探討其界面效應(yīng),加強(qiáng)藥液在葉片上附著效果與葉片接觸特性研究,進(jìn)一步探究APG助劑溶液易于在其表面鋪展的規(guī)律。

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Wetting state and dynamic spreading behavior of alkyl polyglycoside drop on cucumber leaf surface

Zhang Hongtao1, Lu Jun2※, Wei Deyun2, Hu Yuxia3

(1.450011,;2.311800,;3.450001,)

Improving the wettability of spraying liquid on the target crop surface is one of the effective ways for enhancing the utilization efficiency of pesticide. When the spray liquid reached the surface of target crop, will occur series dynamic process including deposition, retention, spread, penetration, etc. These behaviors of dynamic wetting will decide spraying liquid how to transfer to biological organisms, and make directly influence of the pesticide. As entering the 21st century, the dynamic wetting behavior of liquid on target interface has become a very active research direction in the pesticide application field, which is one of the important research contents of precision spraying technology. Alkyl Polyglycoside (APG) is recognized as an internationally preferred green functional surfactant, it has attracted special attention because of its high surface activity and ecological security. In recent years, more and more domestic and foreign researchers have done a lot of work in improving APG pesticide additives, which focusing on the preparation, modification and its synergism mechanism, and achieved obvious achievements. In order to investigate the dynamic wetting behavior of APG additive solution on the cucumber leaf surface and its change of dynamic contact angle, APG solution of 9 mass fraction (14.35%-85.78%) and their dynamic wetting parameters which includes surface tension (), contact angle (), dynamic contact angle (θ), advancing contact angle (θ), receding contact angle (θ), spreading diameter () were measured by using surface tension and contact angle measuring instrument based on hanging drop method and sessile drop method. The contact angle hysteresis and spreading driving force are analyzed and deduced based on Tanner rule, and the relationship curve between spreading diameter (), power value () and time () were fitted by the application of the power law. With digital image processing technology, the process of dynamic wetting was recorded by CCD camera and their dynamic wetting parameters were obtained and extracted from drop images features. The results showed that these 9 APG solutions’ surface tension were within a narrow range from 27.96 to 29.73 mN·m-1, but their contact angle were varied from 11.35° to 34.20° in a wide range. It indicated contact angles did not change radically with the increasing concentration of APG solution. As a kind of easily wetting leaves, advancing contact angle (θ) of deionized water drop on cucumber leaf surface increased by 7.54°, while receding contact angle (θ) decreased by 22.85°, its contact angle hysteresis (Δ) is 46.89° within 10 s. The dynamic wetting process reflects the interface behavior of cucumber leaves accords with the basic law of rough surface contact angle hysteresis. Dynamic contact angle of APG solution of different mass fraction on cucumber leaf surface fell sharply in the first 1 s, then decreased steadily and gradually tended to be stable (1-10 s). The relationship between the spreading diameter () and time () were better conformed to the power law. The power value of APG solution fitting curves were within the range from 0.01 to 0.08, the coefficientwere between 2.787 3 and 3.567 3, the APG solution of lower concentration showed a higher fitting degree. It can be inferred that the dynamic surface tension is the dominant spreading driving force on cucumber leaf surface (interface). This paper provides theoretical basis and technical support for pesticide spraying with cucumber as target crop and APG as adjuvant.

contact angle; wetting; drops;alkyl polyglycoside, cucumber leaf, dynamic wetting, Tanner law

10.11975/j.issn.1002-6819.2017.03.011

S49

A

1002-6819(2017)-03-0081-07

2016-08-14

2016-10-25

國(guó)家自然科學(xué)基金資助項(xiàng)目(31671580);浙江省一流學(xué)科B類(農(nóng)業(yè)工程)建設(shè)項(xiàng)目(浙教高科〔2015〕126號(hào));浙江省自然科學(xué)基金項(xiàng)目(LY16C130008);河南省科技攻關(guān)項(xiàng)目(162102110112);華北水利水電大學(xué)教學(xué)名師培育項(xiàng)目(2014108)

張紅濤,博士,教授,主要從事圖像識(shí)別、計(jì)算機(jī)視覺等方面的研究。鄭州 華北水利水電大學(xué)電力學(xué)院,450011。 Email:zht1977@ncwu.edu.cn

陸 軍,博士,副教授,主要從事精準(zhǔn)施藥技術(shù)方面的研究。諸暨浙江農(nóng)林大學(xué)暨陽學(xué)院,311800。Email:lujun12404@126.com

張紅濤, 陸 軍, 魏德云, 胡玉霞. 烷基聚葡糖苷液滴在黃瓜葉片面的潤(rùn)濕狀態(tài)及動(dòng)態(tài)鋪展行為[J]. 農(nóng)業(yè)工程學(xué)報(bào),2017,33(3):81-87. doi:10.11975/j.issn.1002-6819.2017.03.011 http://www.tcsae.org

Zhang Hongtao, Lu Jun, Wei Deyun, Hu Yuxia. Wetting state and dynamic spreading behavior of alkyl polyglycoside drop on cucumber leaf surface[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2017, 33(3): 81-87. (in Chinese with English abstract) doi:10.11975/j.issn.1002-6819.2017.03.011 http://www.tcsae.org

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